Well, I've owned five cars in my life and three were MGB's; one roadster and 2 GT's. Here's my own list of reasons.
1. MGB's are some of the most beautiful cars you can drive for the money, and better looking than many cars costing much more. The GT6 is pretty close, but too small (for me).
2. They are reliable and easy to repair when they need to be.
3. They handle well and are fun to drive, and can be made faster if you want. The weird thing is you feel like you're going faster than you really are. Which is more important? Feelinmg the experience of speed or actually speeding? Some of my friends with V8's seem to think all that matters is how fast you are going objectively, or how fast you can get to 60. I don't get it, like its really a contest out there? Of course, they never autocross their cars, they just like enthusiastic merges I guess.
4. People check out your car, and its not too intimidating or unapproachable to be asked about, which is fun.
5. The history of the marque, you kind of feel tied into it, and not just to MG, to a whole different era of motorsports and so on.
6. They are definitely British as well as European. A different sensability went into the design then all the cars my family had growing up which I hated.
Many of these are true for many other classic sportcars, but the B is easy on its owner generally. Many people think they are a "cliche" classic car, but you know, its not like I see very many day to day. I think I actually see more Ferrari's than I do MG's.