First is the obvious one that your loaded question alludes to: a resistance to change because that costs so companies won't do it until it would give them a relatively easy advantage (that lasts more than a week) over their competitors.

Second: creating new infrastructure can be a lot easier than upgrading. You don't have to worry about supporting existing devices and userbase.

Third: In developing nations infrastructure projects like that are often in significant part funded by internal government funds and external aid rather than there being an expectation that commercial entities will foot the entire bill.