I'm planning to write a longer rant post about this but since I still haven't gotten around to that yet, I could chime in here. TL;DR: This is an intentional change by SI.
This was one of the "features" introduced in FM21 where some bad 3D renders of rooms were set as backgrounds (e.g. for tactics and team talks screens) supposedly to "increase immersion"somehow by making the functional part of the screen smaller. I brought this up in the FM21 feedback thread (see attached post), but no one in SI cared; similar things were pointed by other users both in FM21 and FM22, but here we are in FM23 once again half the screen is wasted on bad 3D room renders.
My observation at this point is that SI doesn't really care about the users' actual needs and preferences nor takes in their feedback seriously when deciding on features (I wonder how many people asked for this "dynamic manager timeline" for example.); hence I'm no longer as keen to provide feedback to SI in turn as I used to be.
But, I digress: You can fix this screen manually by extracting the skin files and playing around with the values in tactics with embedded section tabs panel.xml in panels\match. See the second thread I posted below for a more detailed explanation. I haven't tried it for FM23 yet, but it should work similarly.