There are advantages to being the one who hosts the playdate. My kids actually prefer if the playdate is at our house as I can tolerate quite a lot of noise and running around, whereas some other mums have more strict rules and get upset if there is noise. Having the playdate at our own house also allows me to observe how the children are treating each other and step in if there is bullying or bad behavior, whereas I don't know how the other parent is handling this if it's at a different house. It also allows me to teach social rules that I like - how to share, etc. Many children have told me they like that they feel welcome at our home. So I don't always mind if parents do not reciprocate.
However if I sense I'm being used as free babysitting, or the other parents are taking advantage (e.g. not picking up the child at the agreed time, being unreachable in case of emergency), or the other parents are unable/unwilling to work with me so that my family is not overly inconvenienced by being the only hosts (e.g. sending their child to a playdate sick), then I stop having playdates with those children. I host when it works for me but I'm under no obligation to be someone else's doormat. It's a judgement call.
As my kids have grown older, the balance of locations of playdates and "get togethers" has shifted, so I've had a lot fewer at my house and there are other parents who have "taken over" the bulk of the get togethers, because their house is more central, an easier drive for new driver kids, etc. Those mums might feel that they are getting too much burden now, I don't know. At the same time, older kids are more independent and it's a matter of reminding them all to chip in some cash if they are going to get a pizza, not so much about making sure 5 or 6 unruly toddlers aren't wandering into the street or choking to death on Legos. Personally I found the toddlers MUCH more exhausting. Teenagers can be loud and opinionated but generally know how to cross the street.