Series in 8 years is an outlier and compared to basketball or football is not that impressive, especially considering they have 1 ring (so far) to show for it.
The Yankees haven't been to a World Series since 2009. The Mets haven't won since 1986.
These teams have massive fan bases to entertain. Why should they not be allowed to acquire as much talent as possible. The A's have the same responsibility and they're not living up to it.