Depends why you want to get users upgraded. If you want your users to be upgraded so they have access to security improvements, and those security improvements require TPM 2.0 or whatever, then allowing upgrades on older systems without TPM 2.0 rather undermines the point of getting those users upgraded.
The secondary goal is lowering support costs. Less hardware to support does that.
Substantially the entirety of the legacy hardware support cost is for accessories, i.e. PCIe cards and USB devices. All of that still exists and people will continue to expect to plug their existing devices into their new PC and have them work.
"Well you see..."
<starts waving hands around wildly>
"If you debase your current OS, you PRIME people for the next OS, Win13!"
<speech devolves into gibberish at this point>