That’s because the clock app does not even try to set it up to wake up from suspend yet. There’s ongoing work to let it do that as an unprivileged app.
It never will. This kind of stuff will be handled by periodic wakeups regardless of whether you’re using cellular data or WiFi.
In general, resuming from suspend is completely unrelated to whether you use the modem or not. The modem only has an additional ability to wake the system up on incoming calls and SMS messages, but that’s all.