Plenty of reasons:
- Strength has been around as an HM for longer so people are more used to seeing it hence the bias
- A 10 base power boost costs 15 accuracy. Not a great trade off. Were the moves of very high base power it would be over looked (Hydro Pump or Fire Blast for example) but it's not.
- It's a Normal type move meaning it's super effective against nothing. As far as normal moves go, Return is generally preferred anyway.
- PP might be higher but most matches end / Pokemon faints way before either PP runs out, so it's not that big a deal.
Sorry for format mistakes and other grammatical errors, on the phone right now.
Edit: As for confusion, that is barely worth it, either: there's only a 20% chance to confuse the opponent. Once confused, the opponent still has a chance of attacking, and if it switches out, it loses its confusion. Therefore, it's not as effective in practice as it sounds on paper. A 20% chance means there's 1/5 probability of confusion getting triggered every turn, not that confusion will definitely be triggered at least once if used five times in a row. Overall, it's not reliable to begin with due to the low chance of triggering confusion, but the low accurate compounds the unreliability of the move.
Edit 2: Inflicting confusion itself is about 20%. Once confused the opponent has a 33% chance of hitting itself. (Thanks KRLW890 and sumwun for pointing that out)
