Both of the above points mean nothing depending on the user.
Comfort has nothing to do with the type of keys uses, that is personal preference.
Keeping a keyboard clean will keep it lasting much longer than you will ever need, regardless of key types.
Mechanical keyboards are so popular due to the tactical responses (audible or clicks). In addition, most feature a better build than other keyboards, but not so much to really be a comparison point.
Another reason is just the mentality, many people think just because they have a "better" keyboard (mechanical) that they themselves are now "better".