You mean "give it *more* debuffing" -- SB already applies a debuff, the Shadow and Flame effect.

yes, more debuffing

SB already renews a DoT (it renews corruption - just like Drain Life does), it applies Debuffs (as others have pointed out.
SB could be made cooler, but ultimately it's like Frost Bolt for a mage or a Fire Ball - it's just a nuke spell, just happens to be a shadow nuke.
And that's exactly why so many affliction locks don't like it - as long as DL can come close to it in the game we'll prefer it, even if it didn't heal (it does help that it heals because survivability is just as important as raw damage - everybody does 0 dps when dead) but it's channeling, it's awesome Soul burn effect - these things add up to, it fits our style and our rotation beautifully.

I know our beloved author says it makes it harder play - I find the exact opposite. Interrupting a half-cast shadow-bolt to renew a DoT is terrible so we never do it anyway, the DL was doing damage the whole time, of course we try not to interrupt it but if we HAVE to move because suddenly we're standing in the fire - it really shines there, we've been doing damage until we had to move, if we were busy casting SB and hafl to run away half-way through, we've got NO damage for the time we spent on an incomplete cast.

That's one side of it - a channeled spell has higher return on cast-time investment than a nuke, always will.
Another is that really the only NICE soul burn that Affliction has is SBn+DL, which is our equivalent of Destro's SBn+SF - if they so badly want us to use Shadow Bolt then they need to give us a Soulburn+Shadow-Bolt to make it worthwhile.
Even if they just made it the same - Soulburn=Instant Cast SB, which we can mix in with the nightfall procs it would make up for it, more instant cast options means the nuke is more usuable, it means less occasions where you spent 1.2 seconds casting, have to run to dodge some boss attack and now did NO damage(appart from DoTs) during that time, while also suddenly having to battle to get corruption from dropping off etc. etc. etc.

Quite frankly, sorry Tyler but you're wrong - a slow nuke as our filler spell is clumsy, a channeled damage spell remains beautifully suited to affliction's playstyle, and if Blizzard wants us to use SB then rather than constant nerfs - they should address the reasons SB fails. In this I agree with the OP - but I dissagree on what makes it fail (because it already does everything he suggested) :P

And here we have my drain life is much harder to play than sbolt affliction. You should never interrupt a cast to refresh a dot, and you should never be doing nothing.

To fill both of these requirements you should recast dots after your shadowbolt cast finishes. You can use the spell queue system here to prevent any dead time.

However with drain life you have to interrupt drain life after a tick. You can't use the spell queue system, you will have dead time unless you play it perfectly.

Thus the weird nature of channeled spells, and the lack of most players in understanding them.