They outsourced that work to Grove Street Games who had already done the mobile ports and said have at it. Grove Street Games took their mobile ports (which were already compromised) and adapted them back to console & PC with a new engine. I assume everything was done on the cheap and to a deadline and what they produced is what they produced. For Rockstar it wasn't a labour of love, it was money for old rope and if they had given a damn they wouldn't have outsourced it or at least had stricter quality controls & acceptance on what someone made for them.

Rockstar made a slightly better job with their RDR port in that they didn't completely fuck it up but it was still outsourced and a minimal effort.