The newest Mk2s are nearly 15 years old now going out of production in 2003 so it's not surprising there are less and less of them about, the ones I do see about tend to be quite rough.
Still quite a few mk2b about but if you keep an eye on eBay these are also becoming less and less, they've not reached that sub £500 point where any expensive bill or MOT failure tends to see them meet a scrap yard rather quickly.
If they had held their value a bit more then people would probably hold on to them. Great little DIY cars but people do less of that now. I even here the number of young people who want to learn to drive is becoming less also.