Upload & Sell: Off
Wonder if they did it because they could (without sacrificing corner performance too much),
because they would (the smaller the better, but sacrificing corners),
or because they had to (best optical solution).
This is a side benefit of the "best optical solution." In the crudest sense, a telecompressor is just a positive lens, focusing the image closer (so shorter overall length) and over a smaller region (similarly, a teleconverter is a negative lens). I suppose a really horribly complicated telecompressor, with many internally cancelling groups to minimize aberrations, could end up longer, but the "natural" starting place is a reduction in overall length.