The LDS church is very emphatic in it's teaching that homosexuality is a mortal sin. Manti may have wanted to make sure his parents weren't ostracized for having a gay son, if he is (not claiming he is or even caring). I don't know that this is the case, but it is as viable as any other explanation.
Truthfully none of the explanations make that much sense to any rational person.
1. Propelling his career - he plays at a very high profile college. All he had to do was play well to be noticed. Did that story really result in him being second in the Heisman voting? I guess it's possible...
2. Cover for being gay - why have one girlfriend for 4 years? Why not have a few for reasonable (he is Mormon) times, like 6-8 months? Then no one would be surprised not to meet her, etc.
3. Thought it would be funny - had to know people would figure it out eventually
and would not find it very funny. And would his parents be inserting their stories
unless Manti punked them too? Though it would explain how a handful of people
have claimed to have met her.
4. Not initially, but figured it out prior to the Deadspin article - could be, and could
have felt trapped into the lie. Would have to admit how dumb he was. But then
why talk about it? Why not just say it was private and that he didn't want to talk
about it?
5. No, he's that stupid - it goes beyond stupid, and really attacks his character.
Doesn't try to visit a sick girlfriend. Doesn't try to attend her funeral. Doesn't try
to send flowers to the service. Doesn't try to talk to her family. Spends 4 years in
a relationship with a girl (even if online only) and never tried to spend time with
her in person? Even as a Mormon, even if he wants to remain chaste, he can still
at least be in the same room as her. Even if he has to have a chaparone present, wouldn't you want to meet her in person somewhere between the first message and
year 4???
It could be a combination. Started off not knowing, then figured it out but stuck
with it to propel his career?
So the conclusion? He's not a rational person. And if I were an executive for an
NFL franchise I would consider that before I drafted him.