There are second order effects as well. Having a good tech blog that talks about this stuff gains the company mindshare amongst developers. If, as in in the case of github, the developers (etc) are the customer, then the translation to marketshare is pretty straight-forward.
When developers (etc) are not the target audience, they still get warm-fuzzies about the company and it gains word of mouth, and non-tech who seek out a recommendation from their friends, will hear about the company with the good blog. Usually in the form of "Oh yeah, there are a couple of alternatives, but the tech at $X is top notch, look hard at them".
Hm yeah, that makes sense. So it's not the case that "[there are] no real reasons" - but I still think it's awesome, and learn a lot/see the applications of stuff learned elsewhere in them.
There are second order effects as well. Having a good tech blog that talks about this stuff gains the company mindshare amongst developers. If, as in in the case of github, the developers (etc) are the customer, then the translation to marketshare is pretty straight-forward.
When developers (etc) are not the target audience, they still get warm-fuzzies about the company and it gains word of mouth, and non-tech who seek out a recommendation from their friends, will hear about the company with the good blog. Usually in the form of "Oh yeah, there are a couple of alternatives, but the tech at $X is top notch, look hard at them".