Turboprops or even piston are a better choice for routes like SB to Burbank than turbofan aircraft; it's just that passengers strongly associate turbofan aircraft with "quality and comfort", so the commercial market loves those.
And, for commercial service under some parts, you're forced to use twin engines. Single engine aircraft are objectively better in a lot of ways, and on par for overall safety (it's better to lose an engine in ideal cases in a twin, but things often go wrong with the recovery procedures, and engines are very reliable, and with twins you have twice as many engines to potentially break anyway...)
Some of the badness is actually FAA not being able to fund better ATC allowing more flexible routing.
Turboprops (and some pistons) are way more efficient at low altitudes. For a short route, most of your time is spent a lot altitudes, so the prop is going to be a lot more efficient. Saves fuel, makes it cheaper to fly, thus lower fares.
Single engine aircraft have been shown to be essentially as safe as twins, at least on light aircraft like these. Engines very rarely fail, and a twin engine light craft failing often fails in a way where the plane still is unflyable, or the pilots of those aircraft aren't able to recover (more of an issue for private single pilots vs. a charter with two). There are some ways where it doesn't matter how many engines the aircraft has, and the twin engines add complexity which increase the odds of problems (which generally cause ground stops or non-crash incidents, but which could possibly cause crashes). Twins also cost more per hour to operate (in fuel, and especially maintenance), and cost more to buy. Inexperienced pilots also manage to crash aircraft with two working engines by doing stupid things with the engines, where they may not in a single, although this is less of an issue with FADEC I think.
For a long flight over the ocean, a big twin turbofan ETOPS certified or maybe even a trijet or 4-engine aircraft is the way to go, but for short domestic flights over land, a single (turboprop, ideally, but even some pistons) would be my choice. My dream aircraft is a CH801 (kit) with a diesel engine (super slow, ~$100-150k), or a Cessna Grand Caravan ($300k and up to low millions if new and highly outfitted).
I remember reading (~10-15 years ago?) that although the general public's impression was that propellers make planes unreliable, it was actually turbines that made airplane engines reliable (which means you really want turboprops rather than piston-propeller aircraft)
Have airplane piston engines become as reliable as turboprops?
I don't objectively agree with the latter point, but rdl is correct about the former. It takes high altitudes for tubofans to come into their element in the efficiency gradient, and short routes don't really stay in that area of altitude long enough to give them an advantage. Turboprops are more efficient at lower altitudes, which is perfect for short hop flights -- where you're spending half of the time climbing/descending anyways. This is partly why Porter Airlines in Toronto flies Q400s.
They're clearly objectively better in a lot of ways; you could just argue that they're not net-better overall, since there are also advantages to twins. Single is undeniably cheaper to buy/operate. Since you never push off without both engines good, there's no way a twin would have higher dispatch rate than a single (since there are ~twice as many parts to deadline your aircraft).
You may still value "has extra engine in case one dies in flight" more than this, though. (and I did, until I saw how singles actually had approximately the same safety stats as twins, at least for private pilots most like what I'd be.)
I wonder if twin-engined aircraft are less better maintained for the reasons you mentioned. Since you only have one engine to 'push off' with on a single, you better make damn sure it's in good working order.
That's ETOPS vs. 3/4 engine aircraft, I believe, but I don't think the maintenance and reliability standards are appreciably different for civilian 1 vs. 2. Mainly because no scheduled service is done using a single engine, so it doesn't even come up.
I'm pretty sure military maintenance standards are so entirely different that their extensive experience with single engine aircraft isn't meaningful -- plus, their singles are mainly either very military specific (F-16 and other light fighters) or historical. Most of their transport aircraft have something in common with commercial, now, except maybe C-130s. And the USN has generally favored twin vs. single for "reliability over water" anyway.
And, for commercial service under some parts, you're forced to use twin engines. Single engine aircraft are objectively better in a lot of ways, and on par for overall safety (it's better to lose an engine in ideal cases in a twin, but things often go wrong with the recovery procedures, and engines are very reliable, and with twins you have twice as many engines to potentially break anyway...)
Some of the badness is actually FAA not being able to fund better ATC allowing more flexible routing.