1) Maybe if you tried using them as long range units with a buffer inbetween or in cover, you would recognize their value in long range combat. Don't charge the enemy with them. Flank, use them to support...
1.1) Just merge them with conscripts, you can keep up dishing out DPS while your foe has to retreat. Unless he can reinforce via HT or Bunker.
2) Because it makes them flexible. After a good flank, they can blow Jerry to hell.
Sure, the unit design may not be as straight forward or clear to some, as in shocktroops or guards. But they can have their place if included in your overall strategy. You don't have to use them if they don't suit your playstyle.
1. Any strat using penals that has to rely on conscripts is ineffective, considering the need to tech for molotovs/AT nades to make the unit half decent. Also keep at range but flank? Choose one.
1.1 Merged models don't get SVTs, so that apparent high DPS that can somehow take out G43s Grens (Really, try Penals sometime, they can't) isn't happening with merge.
Regardless, it is completely obvious that Penals are an overpriced, underperforming unit. I've been playing with them solely for the past two weeks daily, and you either give up a ridiculous amount of map control, or you rely on a similarly underpowered Partisan doctrine, you are at a severe disadvantage using Penals instead of typical PPSH conscript spam.