[imancit]

You know, this is probably a big part of it. On a touchscreen 'haha' and 'hehe' are way easier.

[ajkjk]

I'm confident that this is not why I say 'haha'. 'LOL' or 'lol' sounds sarcastic or at-best ironic to me. Certain people I know still use it at the end of sentences, but I (without meaning to) find it childish.