Not as ludicrous as it sounds.

Before I continue, I just want to state that what I'm about to say doesn't excuse what happened. I'm merely trying to give a reason why the ramp may not have been used.

Health and safety regulations specify how steep an access ramp can be. Depending on the height of the stage, this might mean the ramp needs to be very long. Having a ramp around that was/is used for something else doesn't mean it was necessarily suitable for this use case.

I organised events for over decade up until covid, and the ramp requirement was always a question on my checklist for this exact reason. The blame here almost certainly lies entirely at the feet of the organisers, not the poor sods on the front line who were (probably) provided inadequate equipment.

That's my take anyway