The micro/tiny form factor PCs generally only have space for a 2.5" drive, while the SFF/desktop size PCs can fit at least one 3.5" drive.
Dell, 8th Gen Intel with one 3.5" drive bay: https://www.dell.com/support/manuals/en-us/optiplex-7060-sff/opti_7060_sff_setup_specs_manual/storage?guid=guid-4eab9a0b-c403-4bcd-b692-9419bddfed24&lang=en-us
Lenovo, should have one 3.5" drive bay: https://www.lenovo.com/us/en/p/desktops/thinkcentre/m-series-sff/thinkcentre-m920s/11tc1mdm92s?orgRef=https%253A%252F%252Fwww.google.com%252F&srsltid=AfmBOorJ_EUW-QYIIIGy3i7ZJbitPq8UWoxdoQxtM_BNabrKcNojn7WL#tech_specs
Yes. As time goes on, old equipment continues to fail or get recycled so less of it is available, and there are still people interested for numerous reasons. The CT1350 sells for around $70+ USD on eBay at the moment. 486 hardware is getting more desirable.