The answer to this is a lot more practical in nature than it might seem. It's not a limit imposed by the creators at EA, but one that occurs as a result of the fact that the score is saved in an 8-bit number binary number. This implies that there are 2^8 possibilities of numbers that can be constructed out of an 8 bit number (0-255 in base ten). That's why the score stops at 255. The yardage stops at 1023 for a similar reason. 2^10 is 1024, which implies 0-1023 in base ten. The reason the game is written this way is that, in data storage, 8 "bits" is one "byte." This means that each score only takes one byte of data to store, and the developers probably didn't think it was really necessary to waste a whole extra byte, just to keep the score going past 256, which is quite a ridiculous score.
