...and certainly more difficult to scale than just adding more bandwidth.
but also a lot smarter than sending everything to every car and letting the car discard what it does not need. That simply wouldn't be viable as the number of vehicles and number of software variations increase over time. We also don't know for a fact if Tesla does have some sort of bandwidth throttle contractually built-in to their negotiated agreement with AT&T -- if so, that could account for why WiFi updates hit more cars faster -- assuming they do. Regardless, if I were Tesla and watching my costs, assuming Tesla pays for bandwidth they do use, I'd always prioritize WiFi first.
I personally don't buy internet bandwidth or data centers being an issue --
at least they don't have to be. It's not sexy stuff, but there is no excuse if Tesla is not ramping up support infrastructure as there is an increase in the size of the fleet. You would think Tesla would have the money to do that as the cash becomes available for a slight increase in support infrastructure every time a new vehicle is sold, and they project to the Press and Shareholders how many that is going to be in advance. It could come down to Tesla just not prioritizing build-out of this sort of infrastructure in a timely manner.
Apple e.g. had early problems with significant releases having hiccups and being slow getting to the masses on day of availability, but you don't hear much of those sort of issues these days with specific iOS packages being delivered to tens/hundreds-of-thousands of different iOS devices when it become generally available.
Without any facts to back it up, my own simple conspiracy theory is: I just think Elon didn't like CES and MBZ doing all the EV & Autonomous car announcements they did last week without Tesla also being in the Press and on Twitter. It started to bug him, so he pushed his company to get something out to enough cars that he could do a previously unplanned Sunday (!) press call. Under pressure, I bet the Tesla Development teams then elected to send the pieces and configurations that they had most confidence in or had ready-to-go -- vs perhaps all variations and the rest of the originally planned 7.1 changes many were expecting.
...and no, my S90D here in SoCal does not yet have the 7.1 download, now 2 days after the first one hit the waves.