"However, in a work environment as demanding as the one at Google, it can be challenging to carve out the time to launch projects outside of an engineer’s “day

"However, in a work environment as demanding as the one at Google, it can be challenging to carve out the time to launch projects outside of an engineer’s “day job.”" I.e., give up your 20% time or get stackranked/shuffled out of Google. So it's a benefit that exists on paper for recruiting purposes but which employees are strongly disincentivized from utilizing.