The software being written being slower is of course enabled by those hardware improvements, but 1) the slow software is due to those technical inefficiencies making software easier/less expensive to produce, and 2) we can still make fast software by not using those inefficient means.

That said, there's something of a problem with that though, because by making 1) more and more prevalent, it makes 2) more expensive due to fewer people choosing to work in that manner. Similar to how consumer technology goods get much less expensive, but have many more defects and issues. That "race to the bottom" makes cheap things cheaper, but makes more expensive things more difficult to make. I don't know what that phenomenon is called specifically, but it's definitely something I've been frustrated by in nearly every industry and product category.