They don’t though, or at least not normally, because of the existence of the Royal Rota. The main media groups have an arrangement that they will not all attend all royal engagements in the UK (space and security make it impractical) so they take it in turns to attend each engagement on the strict basis that their material and pictures are shared with all outlets.
This means for the vast majority of the Meghan and Harry’s UK appearances, there will only be handful of media present. It’s also why comments like Meghan that she couldn’t possibly do the school run in the UK because there’d be 30 papparazzi snapping away every day are nonsense (quite apart from the strict rules about taking photos of minors).
The Sussexes and Netflix too I guess are aware that most people outside the UK will have no idea about this, so to tell their story about how “unsurvivable” the press interest is, the press needs to look overwhelming - and generally, it won’t. Hence they use a stock image of another event entirely.
This arrangement only holds for UK media though, so events where the foreign press are all in the UK to cover it - their wedding, for example, there will be large numbers of cameras. Or coming out of hospital with their baby (here’s a shot of just some of the photographers present when William and Kate left hospital with Princess Charlotte). Only the Sussexes didn’t do that, or course.
newsmediauk.org/industry-services/royal-rota/