Why is the PS4 Slim still so expensive?

Do you know why the PS4 (slim) is still so expensive? Actually, you'd have to think that the PS4 would lose value with the release of the PS5, but that's not the case.

Is it still worth waiting or is it still so expensive?

Most likely due to availability. The Ps4 Pro also costs just more than the RRP. Should be cheaper once the situation improves. So as soon as the Ps5 is normally available.