I would just like to point out that Bards are awesome at Counterspell, even though it is not on their list. They almost never have to spend a slot higher the third, as it is an ability check with a max DC of 19 (for a ninth level spell) to counter. Add in a Bard's expertise (not to mention things like Glibness at high levels), and they can be pretty much assured of pulling off a Counterspell anytime it applies. With a third level slot. Only Abjuration Wizards with their 10th level feature compete here.
Awesome at a spell that has little use is still of little use. Divine casters are more susceptible to counterspell than arcane. However, it is usually the PCs that are on the offense in most games. If the PCs are going into a lair they are better served by Dispel Magic and Detect Magic than Counterspell.
So if PCs are able to routinely use counterspell, then the DM is not playing smart spellcasting opponents -- which is fine if your group likes push over/simple encounters. However, intelligent spellcasters in their lairs will only be seen by PCs when they have either run out of spells, they are dead, or through clever play and tactics they get the drop on the spellcaster. In all of these cases, counterspell is of no help.
Take a wizard for example. A wizard can cas Alarm on a choke point in his lair. As a ritual, this doesn't cost any resources but time. In fact there isn't a restriction on how many Alarm spells could be cast other than the casting time and duration.
So if the PCs aren't using Detect Magic and then Dispel Magic to find in place spells, the Alarm goes off alerting the wizard. The wizard then retreats to his sanctum, which is hidden, barred, locked, and Arcane Locked. Knock can only remove one at a time. The sanctum has peepholes and such so the wizard can see out. From that point forward, the wizard has total cover and cannot be seen, yet has total visibility to the rest of the room. Is he doing this because of counterspell? No. This is a setup that prevents the wizard from being attacked at all. By the time the PCs can get to him, he has exhausted his spells and is working on escape.
Even better at high levels since he can just have a gem in a chandelier inside the room of interest and use Magic Jar to possess intruders and using their own against themselves.
My point here is that NPCs, played intelligently, have little concern over counterspell as they have to take countermeasures already against ranged and melee attacks. So again encounter design determines if this spell is useful or not.
So a Bard. Unless the campaign is full of opportunities to counterspell, why would a bard use up a know spell slot on this? It is a spell at best they will cast infrequently. Since this is one of their Magical Secrets, of all of the spells 5th level and below, they are going to take counterspell? Really? Or a Lore Bard with Additional Magical Secrets of all of the 3rd level spells they could take this would be their choice? Really? Out of the 30 possible spells (8 of which can be non-bard) this is the one spell that is the must have?
The Sorcerer. A sorcerer knows 15 spells max, so it seems even less likely for them to learn this spell. The case is the same for the Warlock.
So, counterspell is really only a choice for two spell casters: wizard and redemption paladins (which they get at 9th). So a party that has more than one member that can cast counterspell is an outlier. Even if the party was composed of a wizard, warlock, sorcerer, bard, arcane trickster, and eldritch knight, it would be unusual for all of them to have counterspell unless the opportunities to cast it were so frequent that other 3rd level spells paled in comparison.
Which leads us back to encounter design and frequency of spellcasting encounters. Which then leads back to why nerf a 3rd level spell that isn't used that frequently to begin with because it is situationally dependent?