My therapist has done something similar with me, if he's working a short week or very limited hours. I tell myself that he's pretty sure some clients won't really care about the missed time, whereas I would, so he's offering time to me for that reason. Plus, some are sports psychology clients, so I imagine they may not care as much about missing time (as it's about performance rather than mental health issues--though I'm sure some have both concerns).

I've also wondered whether he says something to clients like, "I'm only going to work limited hours next week--are you good waiting until the following week?" Or "I'm off next Monday--are you OK waiting until the following Monday?" And they say yes. Whereas if they asked about another day, he'd schedule them.

There was a recent week where, due to another obligation, he was only working a few hours each day. He said he could only see me twice to be fair to his other clients, which I completely understood.

To respond to your unease, I just tell myself what my therapist himself has said--that he wouldn't offer something if he wasn't willing to do it. It's not my responsibility to consider those other clients. It's his decision (and potentially theirs).