Why do some departments not offer master's degrees anymore?
Funded masters degrees are getting generally phased out in most fields. They seem to be replaced with unfunded masters' degrees, and/or all students are getting funneled into the funded PhD programs.

The prevailing wisdom (as far as I can tell) is that funding masters students is a waste because as soon as you've trained them to know stuff they leave, unlike a PhD student who you can get a few years of useful work out of. Unfunded programs are great for whacking that international student or trust-fund kid money pinata.