TI-57’s 50 Steps.

[Steve Simpkin]

I suspect the answer is cost and marketing.

Look at the internals of the SR-56 ($180 in 1976):
http://www.datamath.org/Sci/WEDGE/JPEG_S...t%20boards

And the TI-58 ($130 in 1977):
http://www.datamath.org/Sci/WEDGE/JPEG_ti-58c.htm#TI-58

Vs the much cheaper TI-57 ($80 in 1977):
http://www.datamath.org/Sci/MAJESTIC/JPE....htm#TI-57

While it might have been possible to squeeze another 50 steps of program memory into the single chip that makes up the TI-57, it may have cut into the sales of the higher priced TI-58 or SR-56 (which the TI-57 replaced). The TI-57 had the same amount of memory as the HP-25 and competed very nicely price-wise with it when the TI-57 was introduced in 1977. There was no marketing reason to incorporate more memory.