Nobody gets paid to do talks at industry conferences. At least I’ve never been paid for one. Usually you get “free entry” and the like. People generally do this for profile and/or for recruitment.
If i remember rightly, Mark Rein did develop last year? I seem to recall some issue between him and Cliff Harris (although I wouldn’t be surprised if Cliff deliberately stirred things a bit for more press coverage).
Either way, sometimes things like Develop have side benefits, like meeting people who you later work with, or generally getting your face out there. I prefer the US GDC for actual content, but even that is more about the networking and peer stuff (we generally have a big AI dinner before and after the main GDC so we can chat about the job etc).
So for Develop, there are a bunch of evening get-together’s for various things. Simon Barrett (four door lemon) does a good one, but you’ll probably find things by hanging round the bars near the venue (metropole bar had a ton of people around last time I was there).