Why American light tanks keep gaining weight

Was the M41 Walker Bulldog cut short by the underperforming M551 Sheridan?

Not simply; both sit inside a recurring US pattern in which fighting-reconnaissance requirements load so much capability onto a light tank that it stops being light.

The M41 and Sheridan question leads to a criticism of accumulating requirements in American light-tank projects. Airborne use adds one demanding constraint, while other users add capabilities that increase weight. Fighting reconnaissance provides a proposed doctrinal explanation: American cavalry formations were expected to engage more heavily than scouts following the British preference for remaining unseen. A vehicle expected to fight invites more protection and equipment. The expectation of keeping Cold War vehicles for decades also encourages a search for an all-purpose design, with lightness becoming the easiest requirement to sacrifice.