i have encountered this, it's not that they don't care that the code is slow, it's more that they don't seem to have any concept of just how much computing power even a mobile device has these days. i was on a project a couple of years ago, and the client was complaining that something was getting very slow, the original programmer just said "well, that's just how it is, it's only a tablet" or words to that effect...
so the boss put me on that case, and i don't like to blow my own trumpet but, it's fast now.
people don't understand how much power computers have these days. they also don't understand algorithmic complexity, and how it matters *more* as computers get better, not less. as the size of data sets increases roughly in proportion to the size of the memory. if the CPU speed doubles, and the memory size doubles, and the dataset doubles, your algorithm had better be O(n log n) at worst or you're in trouble matey.
i have worked for a well-known manufacturer of FPGAs and the attitude there wasn't any better.