Two reasons -
1. The Aeros buttons were starting to be unresponsive (yes I know there are repair kits and I have one, but ......
2. The Aeros was not controlling the Vu+Solo2 (the most used PVR) smoothly as some commands did not learn correctly - it was a PIA

What I like about the Harmony One -
1. The huge database of Logitech
2. Simpler to set up than the Aeros
3. It learns commands reliably
4. Apart from clumsiness because of small buttons, it is quite easy to use although really no better than the Aeros
5. Excellent Logitech support (vs none for URC)

What I do not like so much about the Harmony One -
1. It is narrow compared to the Aeros with smaller buttons, particularly the navigator ones
2. Macro (Sequence) steps are limited

I looked very carefully at the other more recent Harmony offerings but the only one of appeal was the 650 (nicer key layout than the Harmony One) but it was rejected because I need to control more than 8 devices in the main HT system. But I'll keep my eye open for any new Harmony developments. A Google search has not revealed any better remote for my purposes (HT systems only) than the Harmony one. I got two, hardly used remotes, at a very good price.