Thailand is cheap and safe. They have good infrastructures (internet, hospitals, transportation...). It's hot all year long. There are many expats and tourists so it's easy to find similarly minded people.
Also there are tons of affordable sex workers. Prostitution is not frown upon there as it is in the West. I don't know if it was a motivation for this guy, but it certainly something that attracts many men.
Of course, Europe has good infrastructures. But Thailand is much cheaper than Europe (almost an order of magnitude cheaper for food and lodging).
An other thing that makes Thailand appealing is that there are many expats or long term tourists slacking/working there, so you wouldn't feel out of place living there with no well-defined purpose. I don't think you could get the same kind of vibe in Europe.
As far as prostitution goes, Thailand is VERY different from Europe and the US.
Also there are tons of affordable sex workers. Prostitution is not frown upon there as it is in the West. I don't know if it was a motivation for this guy, but it certainly something that attracts many men.