the REGS 1.121-3 contains some examples where the taxpayer sold after a long period of not occupying it as a principal residence. they moved for a new job. the examples go on to say the taxpayer
is entitled to claim a reduced maximum exclusion under section 121(c)(2) because, under the facts and circumstances, the primary reason for the sale is the change in place of employment.
if you want to read about these look at examples 3 and 4
https://www.law.cornell.edu/cfr/text/26/1.121-3
