Just that it would totally trivialize the content. Why get a four-man group together if you can do it with two?
Some content comes with prerequisites. For normal quests, there's a minimum level. For four-mans, you need a group to do them at-level (though I've found they're doable in most cases with a two-man group already -- my gaming buddy and I have done every one up through Alderaan as a duo, though I've done most of them in four-man groups on other characters).
And they can be skipped if you don't like that level of difficulty. What you're asking for is that these heroics be gimped so that you don't have to meet the prerequisites. I don't think they need to be gimped at all, and that you're essentially asking for content other people enjoy to be butchered because you don't like that particular playstyle. Well, there's a ton of content out there that does cater to your playstyle. Don't destroy mine because you're not willing to meet the requirements to do it, or can't hande the difficulty. Just drop them and move on. Or, maybe even better, try something different for a change and go do them with a group.
Just wow at that last sentence. How many times do I have to repeat myself? I've tried to do every single group quest and I actually do enjoy them when I find a group for them, which is like 90% of the time. The other 10% (like with bonus series heroic 4's) finding a group is almost impossible. Please stop trying to paint me as a casual/solo player trying to strip content away from hardcore players, it's childish and it's certainly not necessary. You also have not answered what's wrong with my second suggestion unsurprisingly.