The real reason is that Bluetooth is awful for data transmission and the bitrate absolutely plummets when there's crosstalk. I live in an older building with a ton of interference on the 2.4GHz band (WiFi, BT beacons, "smart" appliances) and updating any device over bluetooth is impossible.
The new models actually handle update much better. The update is way slower (requires about 1 hour) compare to old model. But it allows you to continue using it while update. (It probably rate limited itself?)
