Because many of us still have our old chargers but more and more have bought wireless chargers.
I think this is a bit of a 2 edged sword.
On the one hand it allows for the reduction of packaging and waste materials such as old charge bricks and un-needed ones but also reduces the freight volume by about 20-30% which has a big impact on the transportation carbon footprint of a product (usually one of the largest contributors to the total carbon footprint for product).
On the other hand you have a £50 reduction in the msrp/rrp for the new generation s21 vs 20 which is enough to purchase both a wired and wireless charger or set of earbuds but many consumers won't appreciate or understand this choice and would rather a choice of a "full fat" retail box and a "lite" version for those who don't need the extras or would prefer to choose their own.
If Samsung think this is a good idea, I'll take a Tab S7+ as thanks 😊