It’s ok to ask something like that.
I'm glad to hear that, as some people do get offended by that. It's really vexing to me personally because I was brought up to value blunt honesty, which is why I can't help but ask in the first place and basically just have to beg forgiveness while doing so and hope it works out.
Now, unfortunately, the particular human behaviour we're discussing isn't something I can confidently explain, only describe, but hopefully I can give you some idea of why people do it. First of all, one of the things almost everyone ends up being taught in dominant Western culture is that hurting someone's feelings, even by accident, is basically
the worst thing ever and makes you a horrible person. So naturally, many (perhaps most) people who live in that milieu experience a deeply visceral fear response, even a phobia, to the idea of having to say to someone's face something like "I don't actually like you and am not interested in further contact". Some people, in turn, have a natural avoidant response to social stresses like that - even imagining going down that road makes them shut down mentally. (It might be surprising, because I'm pretty outspoken most of the time, but this is extremely true of me personally; in fact, I've only just returned
here after having a serious avoidant response about a year ago, though for totally different reasons than what I'm describing.) So what tends to happen is, if you send a person like that a message asking to do something that person isn't interested in... he or she picks up the phone, sees the name/number, feels an immediate knot of dread, might not even be able to read the message, and if he or she does, contemplates responding, imagines it being just so awkward, so much
work to try to come up with a palliative excuse (because 'I don't want to' could be hurtful), probably puts the phone down, thinking "I'll just... answer later", then sees the notification again a few hours later, gets a feeling of 'ugh, I forgot about this', at some point cancels the notification, then at some point it reaches a point where answering would be even MORE awkward because of putting it off so long, and then suddenly a week has passed and just thinking about it in any way becomes a source of guilt and fear and nausea, and it becomes so much easier to just delete the message and try to forget it ever existed.
Of course that's only how it works for some people. For all I know, it could be something else entirely, like maybe the 'she' of the original post is one of those people who just thinks 'Ugh, it's not even worth my time to tell you you aren't worth my time.' But what I just described is probably the #1 reason people find ignoring something easier than answering.