I actually prefer it because I like the GPU to be facing up instead of down in the ATX cases, but the airflow issues have been apparently solved because there are more energy efficient chips available that use less heat
Ummm, sorry but that is flawed logic. Yes, there are many new, more energy efficient components that "generate" (not "use") less heat. But that "less heat" is related to the amount of energy consumed and how efficiently it uses it
in relation to the amount of
work it does. Understanding that relationship is important here.
So yes, there are more efficient CPUs, chipsets, GPUs and RAM too. But many today are MUCH MORE powerful devices able to do much more work for the amount of energy consumed, BUT they still generate a lot, if not just as much, if not even more heat in doing so. So the problem was not "solved" by more efficient components. In fact, the problem was not solved at all.
More energy-efficient components might have contributed to BTX failing to gain traction (at least in entry level, "office tasks" systems). But that was a very small contribution. The bigger reason was price. BTX cost more and money talks.
Another reason is case designers started investing and putting science to work and they started designing cases that provided better cooling. This included moving the ATX PSU to the bottom of the case and in many cases, providing the PSU with its own cool air intake vent. They incorporated cable management techniques so cables interfering with air flow was minimized. The SATA interface became standard, eliminating those big air flow blocking EIDE ribbon cables.
Remember when many of the earlier ATX cases came with just a single 80mm case fan in back and that was it? Case designers started designing cases that supported
multiple large (120mm, 140mm and even larger) case fans in front to pull massive amounts of cool air in, and in back to exhaust massive amounts of heated air out.
Graphics card makers started adding better heatsinks and more effective fan support. Many started making double-wide cards and encased their heat generating GPUs in cowling, or designed the heatsink fins to channel the airflow across those heatsinks and straight out the back of the computer case - making the point the graphics cards were mounted upside down a moot point.
And did I mention that BTX cost more?
