If you pinch pennies buying a spec that exactly meets today’s needs, and next year MS Teams releases a new update that requires more resources, you don’t want to buy a whole building full of new computers.
(I don't mean that IT departments hand out bottom-of-the-barrel plastic laptops which break every five minutes, but rather fairly low-spec Thinkpad/HP/Dell business laptops with just enough RAM that their bloated Windows 11 installs are barely not swapping when idle and just enough SSD space that Windows Update doesn't fail)
The pricing difference between an i5 and an i7 aren't really that big when you go to Dell and tell them I need 4,000 desktops. DHS isn't paying the same pricing difference as we would be when purchasing a boxed CPU.
Bureaucracies generally need to spend all their entire budget to show that they "need" it to avoid losing it next year, so they are certainly going to spend it. (Also, expect increased corruption)
personally I have an i7 in the lab that turned into a crawl on Youtube because they started sending VP9 video by default, but i7 doesn't have hardware decode for it. Got a plugin to force h264 (h264ify) and it's back to normal.
Then you have situations where a software update adds a CPU instruction dependency and straight up doesn't work anymore.
Had to install and force-retain an old version of Spotify client on a bench lab PC because the new versions require AVX-1/2. It's a streaming audio player...
Well, an 128kbit MP3 requires at least a 486DX2-66 but you also need to run the OS. /s