This is quite subjective. Sugar and salt make things "taste better" if you already have a certain expectation that that's how food "should" taste. That's not the case if you don't have that expectation.
I gave up buying products using refined sugar entirely for an extended period, and baked all my own bread, oatcakes, biscuits etc. Food which I previously found unpalatable without adding sugar or syrup, I could now eat and find perfectly tasty. When I cook porridge in the morning, water and a touch of salt are all it needs. I think it recalibrated my taste significantly--if I now try to eat even a biscuit from a supermarket, all I can taste is the excessive amount of salt in it. Likewise anything with refined sugar--it's too much, and it tastes disgusting. I think with industrially-produced food, we've become so used to the excessive amount of salt and sugar, that it has become normal to expect it even when it's unnecessary and things taste bland when they aren't included--even though it's perfectly fine. You're likely right it sells better. But it's like the music "loudness war" but with ingredients; the end result isn't that enjoyable or good for you even though it seems superficially better.