What you're describing is real, and it's nobody's fault, but that doesn't mean you have to just stand there watching it fall apart. The thing is, they're in a different phase (stress, weird schedules, exhaustion) and you have to reinvent how you stay connected too. It's not about giving up, it's about being more creative with how you get together.
Here's something most people don't mention: create a WhatsApp or Telegram group where you share everyday stuff without needing to actually meet up. Memes, news that makes you laugh, photos of what you're doing, random questions... it keeps the connection alive without the pressure of "we really need to see each other." It works because they can interact whenever they can, with no commitment to blocked-off time. Then, in terms of actually meeting, try getting together in smaller groups instead of all at once, and sometimes include their kids if possible (a relaxed meal, a walk). Some people love having another adult around who isn't family.
What hurts right now is the transition, but the friendship doesn't disappear if you accept that rhythms change. Plus, in a few years some of those kids will grow up and have more independence, and you'll have more breathing room again. It's not permanent like this.