I have a set of SES AR 4.5s. My understanding is this has to do with bead diameter, profile and stiffness. Giant, Zipp and Corima all sell hookless rims and all have published similar lists. I'll bet you can use any tubeless ready tire you want without issue, Enve just wants to ensure 100% safety. I blame tire manufacturers far having varying bead dimensions and not sticking to ETRTO more than Enve for being picky here. Personally, I wanted to use Gravelking slicks anyway and they're on the approved list.

I have multiple sets of both hooked and hookless wheels. They are functionally the same in terms of mounting tires and maintaining pressure reliably. All things being equal and if the industry could settle on a bead standard here, I think hookless is a superior setup to hooked beads:
1. Hookless is likely stronger than hooked beads with the same amount of material as it's just a thick wall of carbon instead of an cantilevered hook. This is really tough to prove in the real world, but certainly the hookless walls on the SES ARs are reassuringly beefy.
2. Allows a noticeably broader / more straight-walled tire profile at any given internal rim width. This is both cushier and (slightly) more aero. This is not just theoretical, the 32mm GKs I'm running measure at 34.5mm on the rims and have a very broad profile. The resulting ride is terrific.
3. Significantly cheaper to manufacture, although this doesn't really matter with Enve. Zipp does credit the price drop on the 303 with moving to hookless.
4. Can be significantly lighter. Zipp has said their hookless 303s are apparently 300g lighter than the hooked version.

One thing to note is you can't run anything close to a high pressure on hookless rims. The SES ARs have a max pressure of 80 psi (I run about 40 psi on the 32s) and Zipp has a maximum of 72 psi on the 303s.