Doesn't almost every T&C around the world specify that redemption tickets are for the base ticket only; surcharges etc. are paid in cash?

There are few exceptions to this that I know of (e.g. QF Any Seat Awards, where the surcharges/fees/taxes can be paid with points).

And almost every FFP around the world hardly yells out in their marketing "Use your points to redeem for free flights!" and then even tacks on a fast-talking rider that it doesn't cover your fees, taxes and surcharges.

In some cases, the fees/taxes/surcharges are not that huge, and especially if booked in a premium class, the effect is lessened. But in other cases the fees/taxes/surcharges are a significant part of the total ticket price (base fare fairly small), so it's not worth blowing points for the redemption/award ticket and you might as well buy it in cash.

A couple of things that most newcomers may not know, and whether it is up to the airline to explicitly say this in big marketing letters is debatable. The first is that award inventory is limited. Just because there is space in the cabin physically doesn't mean that you can get that seat as an award. The second one is that, and I don't know about BAEC, some FFPs (QF again) preferentially open more reward seats for their most elite flyers. It doesn't mean that an entry level member can't redeem a F or J award, but it would be markedly more difficult for them to do so. And it is in the premium awards where the value of redeeming points is really realised.