Why Did FlexATX Flop?

There are full-featured, modern FlexATX motherboards: The Kontron KT965/FLEX supports current Intel desktop CPUs, four DIMMs, four expansion slots, and lots of I/O. The Tyan Toledo i965R S5180 supports two DIMMs and two slots. Kontron and Tyan also offer a few other FlexATX server and embedded boards. However, much of what a web search turns up are yesteryear's out-of-stock models.

So FlexATX did not flop entirely, it seems to have enjoyed some popularity and then faded into a niche. What happened? Did CPUs become too hot? Did Intel de-emphasize FlexATX when it created BTX? Did consumers not care enough about size? Or do those who do care about the size of a PC simply choose a laptop?

Does anyone have any insights into the rise and fall of FlexATX?