The reasons are numerous as to why you need to do some hypertrophy work.
For me? Multiple muscle tears, wasting disease, and the hate for doing anything other than the core lifts that make your head want to explode on every rep. I have multiple shoulder, bicep, and lat injuries AND I need to gain some more size just to be better in my power lifts and Strongman Events BUT I don't want to spend an entire training session on arms or lats or inner outer quads!
What I've been doing for the past few months is setting up a Tabata Timer on my phone in different combinations.
Here was me doing 12 Seconds Work, 12 Seconds Rest, 12 Rounds for Triceps, then Biceps, then Shoulders, then Lats. Took me no time at all and I was fried!