It's maturity. Happens with everything. You just don't get fired up anymore over a lot of other things either like cars. A car is a car. I'm not out there cleaning my brand new car barely at all. Why because I've had too many. Same with gear. Still nice to have and enjoy.
The only way to forget you had an amp coming is if you were so preoccupied with something else way more important and time consuming or you have a memory problem you might want to get checked for. At least I would be concerned for myself if I had no memory of buying an amp.