In our experience, a large proportion of those that don't offer general help are people who need that time.
Maybe they are not coping well with their toddler at home and need to get out the house
Maybe they have no adult conversation and are grateful for the friendship they find at Toddler group
Maybe the only time their toddler/baby isn't screaming is when occupied with the toys at Toddler group
Maybe they don't have the finances to provide many toys at home
Maybe they are very shy and afraid to stand up and be noticed
Maybe they are afraid of putting things in the wrong place and looking stupid
Maybe they are just so physically exhausted from no sleep that they have no energy
Maybe they are mentally exhausted from other stresses in their life and value being able to just sit
Maybe they are struggling with the responsibility of being a parent and cannot cope with any additional responsibilities
... Im going to stop now. I have millions of other reasons I could continue to reel off..
Point is, it is often the people who don't tidy up that are most in need of coming to the group.
Making these people feel shitty is likely to ailenate them from a group. Yet they need the group a lot more than your average "let my child play while I have a cuppa" crew.
It's uncharitable to be mean.