Cost/benefit matters. Concentration is a high cost but 5e is designed so the benefit of that spell are not needed and failure on a roll doesn’t really matter.
You must be playing your games very differently to me.
Recent example. My level 11 paladin (+12 to hit) was fighting a mixed group of enemies. We knew there were some sort of shadow demon things among them, and the group planned for my PC to focus on them because they were vulnerable to radiant damage from smites. From previous combats, we knew that the demons weren't difficult to hit, so i was using Great Weapon Master. We didn't have sufficient prep time before combat for me to cast Bless as i would have, in an optimal situation.
My dice deserted me. I rolled low single figures three times in four attacks over the first two rounds of combat. This was a big deal in the context of the combat. Not only did the demon I targeted survive to get an action off (and drop an AoE on us all, causing loads of damage, some of which might have been avoided if we'd had that +1d4 on saving throws...), but that meant i had to spent the next turn finishing it off, which meant an assassin got through to our archer who then had to stop shooting and defend herself in melee, which in turn meant she couldn't shoot the mind flayer off the cleric. A Bless, and I would have one-rounded the demon, and been in place to smack the assassin down before it got into our squishier characters.
I'm aware that 5e maths is designed so that PCs hit significantly more often than they miss. But 'hit significantly more' is NOT the same as 'never miss'. I only had a ~20% chance of missing that demon. That's not large, but 20% chances do happen. Repeatedly, in some cases. Turning that 20% into 10% is a big deal. The first failure didn't really matter, but combined with the subsequent ones it sure did.
Plus, in the specific case of a paladin, I'd argue that the cost of using your Concentration is not really very high. You often want to be saving your spell slots for smites, so casting a spell once and then getting lasting benefit from it is good resource use. Plus, Bless is only level 1, so you can save higher level slots for
bigger smites, which can have a major impact especially if you land a crit on something.