Every person I've ever seen using VDI has a company PC plus a virtual desktop, so there's no cost savings there. The main advantages I can see are easier backups and not having to worry about network bandwidth too much (just enough for RDP is good), but there are drawbacks too like dealing with remote printing, a lack of support for hardware security tokens, etc..
For example, try to get a YubiKey working [1] with WebAuthN or FIDO when using RDP / VDI. It's basically impossible and you're stuck with crappy 2FA like TOTP.
I've spent way too long reconfiguring yubikeys to act as an OTP device so that they work over RDP.
(edit: reconfiguration is needed to capture the device ID/secret and get them registered to our MFA provider as an OTP token, I realize they do OTP OOB :) )
I'd need more info on the service, but I'd imagine this is very cost competitive. As to "why?" - because for things like HIPPA data, I'd MUCH rather have my doctors/IT staff logging into a remote desktop session that I can lock down so if their laptop gets stolen from their car I don't have to worry about whether or not some day someone will be able to crack drive level encryption. Or worry that an employee didn't have drive level encryption for some reason. Same for financial institutions/etc.
Furthermore a doctor or insert staff can connect from home, and I don't have to worry about whether or not they properly secured their home desktop. Yes there is still some attack surface there, but far, far less than them storing files locally on their home PC.