What does "Waveport" signify in CST/HFSS in antenna design?

Hi,
When we design an antenna in CST or HFSS, we define "waveport" at the feeding terminal with a "rectangular cross section".

But practically we feed the antenna by SMA connector connected with a 50 ohm coax.

My question is why these EM software use "waveport"? Why don't we just place a SMA connector in CST/HFSS and simulate?

I read about it in documentation that cross section of waveport is regarded as a cross section of an infinite rectangular waveguide connected to antenna but in practice we are NOT feeding the antenna with that rectangular waveguide. So, why assuming this?

Please do not refer me any CST/HFSS documentation because I have read them and got lost in the middle of their professionally-curtailed language presentation.

You could make a coax cable using cylinders and define the inside dielectric as the wave port surface. Then normalize the waveport to 50 ohms and you should be able to match your SMA.

Yes, we can always do that.
BTW I had another explanation earlier this morning from one of my friends. He said although practically we feed antenna by coax but in EM simulator we simplify it by a rectangular cross section (waveport). In fact coax and rectangular waveguide both have similar characteristiscs in term of wave propagation. So wave port is just an abstraction mechanism of wave propagation through coax to antenna.