The thing is, babies need supervision at soft play, whereas older children really mostly don't. Older children may be part of the reason that babies need supervision, but it's not as though you could just sit and have a coffee while your 1 year old toodles about, so is it really that hard to say 'This area is just for babies' or 'careful, she's only little' to an older child every so often? I know that you think that their parents are lazy, but they are genuinely just giving their children age appropriate freedom in a safe place, and there's no reason to believe that they will take offence if you have to remind their kids of the rules (I have been on both sides of this, and things have never kicked off, even at some of the more 'questionable' soft plays!).
I know that big kids seem wild and irresponsible when yours are tiny, but as they get older, you realise that they get bigger quickly, but it takes a while to develop a proper sense of 'safety' and 'being careful', way beyond the point where their parents can realistically chase them around a massive play frame, keeping eyes on them every second.
I remember how big the 'big kids' seemed when mine were tiny, and I look at mine now and wonder when they will learn to think things through (and I know my friends with older kids are still wondering!).
Soft play is like the circle of life in a nutshell - one day you're standing watch over your tiny little cruiser, then you are trying to let go as your little adventurer wants to go off and explore by themselves, and then you have a proper 'big kid' who helps the little ones and you know you can rely on them to be sensible...99% of the time.