According to the info re e-sims
The esim pack includes a voucher with a QR code which you'll need to scan using your phone’s camera. This will download an esim profile to your device. The esim pack gives you step by step instructions on how to do this.
The esim pack also contains the Sim Serial Number (SSN) of your esim profile, which you'll need in order to move your existing mobile number across to an esim.
Veritas Numquam Perit
Unfortunately, we cannot answer for O2's decisions......
I know EE will email a QR code but why O2 won't is beyond us?