You were unhappy there were no advancement opportunities so you started looking?, OP is saying the same thing, if it was perfect people generally don't look for new jobs.
It is not because of loyalty it is because we are risk averse, a new job is a lot of risk. Many things can go wrong you may not like that new job, or even purely financially it can be risky as a new company may not pay as promised, shutdown, you get fired pretty quick and may not find a job at same compensation , or variable/ equity compensation wasn't as good as promised/imagined. All of these scenarios have substantial financial risk.
To take that risk(even if only financial) there has to strong motivation.
If I could have stayed doing the same thing I was (software development) for more pay I would have stayed. Might have gotten a bit stagnant/boring in a few more years but I would have been happy until then at least. The only potential advancement opportunity (salary-wise) would have involved changing over to being a DBA or a sort of DBA/developer hybrid role which would have been interesting (I would definitely prefer the hybrid role to being a pure DBA) but some statements from higher-ups about hiring freezes etc. made it clear that wouldn't happen any time soon (even though my direct manager was supportive and trying to help).
It is not because of loyalty it is because we are risk averse, a new job is a lot of risk. Many things can go wrong you may not like that new job, or even purely financially it can be risky as a new company may not pay as promised, shutdown, you get fired pretty quick and may not find a job at same compensation , or variable/ equity compensation wasn't as good as promised/imagined. All of these scenarios have substantial financial risk.
To take that risk(even if only financial) there has to strong motivation.