Many people doing this are
a) older now, and in accordance with that change in time of life tend to have more commitments and less time
b) and less patience for bullshit behavior on the part of others.
They have to pick and choose how they spend their time, and naturally want to have as much fun as possible in the limited time that they have. Family obligations, careers -- sometimes scheduling way out is the only way to make that time. Many of us have been doing this since the nineties, and have favorite friends to play with, too.
I've met brand new people in the last few years that I'd never met before who have become routine favorites on my list of people to play with, and all it took on my part was going to events and inviting people to do things that I thought might sound fun for them. Paying attention to what people like doesn't mean you have to become lifelong friends or pitch your character as something they are not, but yeah, if you want someone to block out time for you, it makes sense to have an idea of what you'll both find fun. That's courteous, and more likely to get you the long-term options for RP you want, anyway.
The hidden difficult truth here is that sometimes I hear people talk about how they cannot for the life of them 'break through the cliques' or get RP, and I'm not sure how to tell them that it's because they're incredibly irritating human beings, either through selfishness or some other unfortunate quality. Nobody's got time to life-coach strangers. (I'm not saying this is you. I don't have any idea who you are. I'm just saying, it happens a lot.)
tl;dr: Things changed because a lot of us grew up, and some of us did not.