Please tell the ignorant, why do these cars have pantographs in the back, and not in the front?

This is historical.

https://transphoto.org/articles/4349/

Trolleys were used until +/- 1963 (see historic photos). When they switched to pantographs, they opted to place them at the back, which roughly corresponds to the position of the contact of the trolley. This had everything to do with the electrical operation of the points via the catenary.
The advantage was that one could leave everything as it was.

Now it does not matter, and in the low-floor trams they also hang in the middle, which is very neutral in the two-way versions.

Ps the first PCC's were delivered with trolleys and not with a pantograph (also in Brussels).

Wow, very interesting. Thank you for telling me.