Why are table slats not at 45 Deg??

CNC plasma is all new to me, but I see lots of posts about problems with cutting the top of a whole slat of it lines up with the cut.
Some solutions call for bowed slats, others I have seen have points sticking up from the slats.
There must be a reason why the slats are not made at an angle to the x/y travel??
Thanks
Keith