I agree that it shouldn't happen. I certainly know friends who's parents put a lot of pressure on them to leave and at least threatened kicking them out. It has actually happened for real to at least one member here- as far as I'm aware.
As for why. I think it probably depends on the parents. Some likely don't give a shit and want shot of their kids asap.
Some may genuinely struggle to afford it. Whether that's their fault is debatable I suppose. Personally, I hold antinatilist views. I don't think it's fair to bring children here and basically just enlist them into wage slavery the rest of their lives.
That said, it seems like the majority of people do seem to accept it. More than likely, your parents accepted their 'responsibilities' too. Do you know what age they started to work? So reasonably or not, I think they often have the same expectations of us. They don't even see it as an unreasonable thing to ask of someone. I suppose they grew up in a culture where you were expected to pay your way in life as soon as you can. Again, not saying I agree with it. Just trying to understand why they have these views.
Also, some of it may be to do with a genuine desire to see us happy and fulfilled. Not meaning to be cruel but, how many NEETS here feel really good about their situation? Some definitely do and, that's fine. Some don't at all though.
There are many who are now feeling even more stuck because they feel like they missed their opportunity to progress in life or, that they now have a strong sense of missed potential. Not saying a person should feel this but again, I suppose our current culture tends to push that one on us.
Also, there's the issue of aging and mortality. All our parents will get to a stage where they can't work and eventually of course, they'll die. If we're not self supportive by then- I imagine they will be very worried for us. So- they may see it as being cruel to be kind forcing us onto the employment ladder early on.
Obviously, a gap year isn't the same as 5,10, 20 years but, maybe your parents are frightened it will turn into that. They may also genuinely be concerned as to how they will fund that. Presumably if they can't, you all suffer. Again- still not reasonable they would kick out their child- now adult because of it but, maybe understandable that they're frightened for all of you. If they aren't able to bring in anymore money, the logical next thing I guess is to pressure their child to.
Also, in terms of when you do go for jobs, sometimes they will query gaps- as far as I've been told. So in general, I get the sense it is wise to at least have a solid sounding plan for them- to gain work experience, to travel etc. Not sure whether it's actually true that employers don't like to see gaps on a CV but, that was always impressed upon me.
I think there are multiple reasons parents don't like it. Maybe some of it is plain old jealousy. Did their parents fund them for a gap year? Most likely not I imagine. But, I agree, to actually throw a close relative out seems so callous.