FIFA and PES manage to find a way...
I didn't think it'd be you that I'd need to make the 'DBC isn't FIFA' point to. They would have teams bigger than the whole development team of DBC14 that could work on what custom modifications they would officially allow, to deal with reports of infringing/offensive content, etc. It's a scale thing.
Besides, my understanding is that they are basically just supporting custom sliders, and no real deep gameplay editing - certainly not changing config files like you can on PC.
And to address custom sliders - obviously it's a matter of minimising the testing matrix in the early editions of the game. It's hard enough getting things to be balanced and work out the bugs with 5 difficulty levels with a team the resources Big Ant would have - needing to have consistent and reliable results with that level of supported customisation would need a lot more testing.
If people download something within the game - they'll blame the game for the problems. Hence complaints to Big Ant about the quality of what are created players in the Cricket Academy. There's a lot more work Big Ant need to do on the five difficulty settings and existing AI before they start officially offering up user created modifications to it - because they'll get all the complaints when people's edits go wrong.