OP, I hear you. I don't think you're unreasonable.
Can I advance another theory? I have a friend similar to yours. She works a 9-5 weekday job, no partner, no kids, no dependents. She lives in a small, low-maintenance apartment. She goes to church once a week, but (aside from work) that's the only commitment she's got.
And yet... whenever we make plans for a casual coffee, she normally asks for a date that's anywhere between 3-7 weeks in advance. That's because (in her own words) she likes to space out her social events. As she has a somewhat limited social life, she tries to avoid a situation where she sees 3 friends (separately) in one weekend, then sits at home by herself for the remainder of the month. So (for example) if she's arranged to have coffee with Friend A for Saturday June 8, and Friend B invites her for brunch on Sunday June 9, she'll push back Friend B until the following weekend.
Most of the time I just roll with it. Where it becomes problematic is when we've arranged to have a casual coffee weeks in advance, but then something comes up in the interim for the same date/time that I'd much rather attend. (For example, one of my favourite authors unexpectedly comes to town to give a one-off talk, etc). It then means I have to forgo the event I'd rather attend, because it would otherwise mean cancelling on my friend. And when the coffee date has been planned so far in advance, it somehow feels ruder to cancel, if that makes any sense?