I must admit I've been guilty of repeatedly not reciprocating invitations with a few of DSs friends. First reason is that I'm ashamed of our home in comparison to our friends. We currently have 4 people living in a very small 2 bed flat, and my friends all seem to live in houses with gardens.
Second reason which is slightly related - their children don't understand about small space living as they are not used to it, so they do things like swinging things around and knocking everything over, jumping up and down a lot (downstairs neighbours go ballistic about this), pulling everything out - ie all the toys without putting the last lot away - which in our flat is just not possible, we don't have the space for it. The children also comment to DS 'why aren't you in a house? Why don't you have a garden?' constantly - totally innocent on their part but he has had a cry after they've left a couple of times. They also don't understand that if they break something we can't afford to replace it - for their parents if something is broken they go to the shop and get a new one. So they are a bit 'grabby' with the TV and computer and suchlike and I don't think their DPs understand why I'm so stressed about them grabbing things. Their DPs don't tell them off because I don't think they understand either as they have never been in this situation.
We also live a bit further away from the school which makes pick up/drop off more difficult - three of DS's friends live literally opposite the school so if they say 'want to pop into ours?' as we come out of the gates I sometimes say 'yes' but inviting them to ours is a bit more of a production.
And then there's behaviour which I've slightly touched on above. Some of my DSs friends are so badly behaved that I don't want them at mine, but if I get a repeated sincere invitation for DS to go to theirs and DS really wants to go then I'll take them up on it.
And finally - I don't like DS to have too many playdates. If I reciprocated all of them then he'd have two or three a week, and it's just too much.
I have never invited DS to someone else's house though. I usually only say 'yes' to him going to someone's house after repeated specific invitations.