Facebook, Google, Apple, Microsoft, IBM, HP and many others would certainly not agree with you. They cook their own food, own lot of real estate and I am pretty sure they don't think it's time they lost.
These big companies do not manage one single house (office). They manage a real estate portfolio. Most of big companies have a mix of rented and acquired office space. Ultimately, owning real estate or not is an investment decision.
Some big companies, like HP recently, went from owning most of its real estate to sell large chunk of it ... Reason is to get some cash flow and to rationalise some expenses. But not because someone else could manage better their real estate.
It's not just real estate. I'm not sure about today, but in the 2000s when I worked at Intel, they owned their own jet planes. They had so many employees flying between certain cities they had locations in, that it was more cost-effective for them to operate their own mini-airline.
Outsourcing stuff always costs more, because you have to pay for the profit of the company you're outsourcing to. It's worth it when it's something you don't do that much of, or aren't very good at, but if you do a lot of it, it's worth it to do it yourself.
For an extreme example, think about printing: is it worth it to outsource all your computer printing needs to a specialized printing company? Or should you just buy a laser printer for $100-500 and do it yourself? It doesn't take very much printing for it to be a massive waste to pay someone else to print stuff for you.
That's because they have a lot of superfluous capital and cash flow that needs investing somewhere. If your profits aren't like Apple's it's often smarter to rent and use the capital for something else.
These big companies do not manage one single house (office). They manage a real estate portfolio. Most of big companies have a mix of rented and acquired office space. Ultimately, owning real estate or not is an investment decision.
Some big companies, like HP recently, went from owning most of its real estate to sell large chunk of it ... Reason is to get some cash flow and to rationalise some expenses. But not because someone else could manage better their real estate.