For me its appearances versus reality. When I first got into the industry, I worshipped the chance to work at Google (or Facebook, MS, etc). I've since stopped worshipping and now I would not take a job with them. Often I wonder why my mind changed over the last 4-5 years but it comes down to the fact that I've seen how the industry works. Google is very much like any other megacorp, just with an extra coat of prestige to make you want to work there, even though it is prestigious, that prestige isn't going to make the problems that megacorps run into go away.
I'm sure they have infra issues, I'm sure there are messy ass codebases saddled with tech debt everywhere, I'm sure that there is going to be scant documentation and you're going to go on the journey of talking to multiple teams. When I was younger I would have said: "but it's google, they must have figured it out". Now that I'm older I say: "but it's google, no way they don't have these issues, no thanks".