How come the Dayton Audio DTA-1 disappeared?

It was build around a very old Tripath chip that even Tripath did no longer manufacture long before they went out of business, that's why
Lots of cheap class D amps nowadays. Anything from aliexpress with a cheap TPA3116 chip on it will perform at the same level as these old Tripath amps, can be bought for around 10 to 15 dollar for a stereo board. . It's not highend though but certainly a lot of value for money.