Why aren't Stata's .dta files backwards compatible?

I work on a few servers with different versions of stata (mostly 13 and 14, one with 12) installed on it and have a hard time referring to datasets across servers because files produced on 14 can't be read on 13 and 12 and so on. Is there any other explanation (besides planned obsolescence) for this? Is there any downside to using saveold rather than save everywhere to solve this problem?