" if one is worried about plant size, why not just get an indeterminate
plant and prune to a certain size which will keep producing fruit?"

Because generally the tomato plant only grows new tomatoes in new growth areas near growing tips. If you tried to restrict an indeterminate for a long time into a specified small space you'd severely lower it's production potential and make it bushy, because you'd be continuously removing new stems and setting the plant back to start over, whereas the determinate gives the benefitof funneling its all to that same space in an abbreviated time frame, and you dispose of the plant when production becomes sparse.

There are shades of determinism in plants though and a "semi-determinate" might be something to look into. This all said, pruning is a common method of finding a compromise with indet's and is commonly done of course, at least, since the French elevated it to an art form 200 years ago.
PC

<so why on earth would i grow determinate again?!?! ;)>

In addition to the info PC posted, the simple answer is that getting an indeterminate and pruning it to a certain size won't work. Many try and many fail as it is totally contrary to the nature of the plant or any vine for that matter. The more you prune the taller it gets and the less fruit it produces.

You'd grow a determinate to get that particular variety. You'd grow a determinate is you have limited space or smaller containers only or you prefer to only deal with shorted plants for some reason. You'd grow a determinate if you wanted lots of tomatoes at nearly the same time as for canning or making lots of salsa.

Many plant indeterminates and then panic when it gets taller than their little cage or wider than the 2 feet they allowed for it and they want to either chop off the top or lop off branches. They don't understand the nature of indeterminates and try to force the plant to meet their expectations rather than adjusting their supports and spacing to the plant's needs.

Dave

It took me years to get to this point: Determinism in tomato is a growth habit. While indet branches ( main or side) keep growing "vine like) for ever, det branches , otoh, is terminated by flower truss.
Another distinctive feature of determinant is that 2 consequtive flower clusters are more closely spaced, with 2 leaf branches between them (approx). while there are 3 -4 leave branches between trusses in indet.
I find it "NOT TRUE" stating that determinate flower/fruit in one shot/flush and then is finished.
Firstly, not all the trusses in a given branch flower/fruit at once. secondly, there will be new branches kicking into production. I have had determinant that kept producing like indets all season til frost. . They call these "semi-det " or sometimes " a det with indet fruiting habit".

YMMV
Sey