well first off, the question implies that we all have an option- for many who are stranded in rural areas, or in crappy cities like my cincinnati lol, there really isn't a gay nightlife to explore.
that said, IF one has the choice, it could further boil down to whether one is more of an introvert or an extrovert. personally, i hate being in a loud room full of hundreds of people- others thrive on it. if i want to go out and be seen, i'd rather it be somewhere neutral... not so saturated with... expectations. overwhelming parties and being swarmed with strangers just isn't my idea of a fun time.
for still others it boils down to the 'lifestyle,' -clubs/bars are pretty damn gay lol. not a bad thing, just not everyone's cup of tea. from the 6'+ drag queens lumbering around, to the twinky manarexic little boys in girls tshirts, to the old queens and those who WOULD be attractive if it weren't for their flamboyant clothes, hair and attitudes...... well, im sure its fun when you're drunk but honestly its not terribly conducive to finding 'the one.' any more so than the internet is. for that matter its not really superior in 'connecting' with other gays. i feel i connect better to guys in here than i could if i met them in a loud crowded club. but yeah there are a lot of gay men out there who just don't get into the whole 'scene' described above- not because they're closed minded, but because they just don't like it or feel comfortable with it.
and finally there's the convenience factor, in choosing the internet as a platform to meet men over clubs/bars. some people can and do get dressed up, liquored up, and hit up most nights of the week at clubs, but that lifestyle's just too exhausting for some... who prefer to sit with some hot tea or good wine in the comfort of home when looking to connect with other gay men.
a final thought- are people any more 'real' or honest in clubs than they are online? sure they don't have the benefit of photoshop, but dishonesty wasn't born with the creation of the internet lol