Part of it is that many of these abilities aren't terribly useful.
Starting with the level 1 ability. It does only two things. It gives the warlock a bonus to perception, and it allows them to cast spells from the space of the bound creature. They can set up the bound between 3 or 4 times a day, and it lasts an hour.
Now, casting from someone else's space does have some uses. I won't deny that. But, the example of binding the rogue and letting them scout probably doesn't work. Because the tether is visible (so the guards or monsters might wonder why a string of fire is hanging in the middle of a hall and follow it to either the rogue or the party) and while you can cast from the space, you cannot see from the space. So, let us say that the rogue is ninety feet ahead, and sees a cave full of goblins. It would be awesome to cast Hunger of Hadar into that cave and mess them up. But you likely can't. Because you don't know the spell is ready to be cast, you have no way to communicate with the rogue.
Weirdly, another limitation I thought there was was the limitation of spells being cast "to a point you can see" but both the examples I looked at (Hunger of Hadar and Shatter) just have something happen to a point within range. Which is odd, since that would allow you to cast through a closed door. But, I'm sure these are anomalies. Generally, you have to see the target to cast the spell, and that still applies whether or not you can deliver the spell from the bound creatures space.
The only two improvements on the bond include granting resistance and the Protective Wish.
The resistance is decent, it covers you and one ally. But the wish is odd. Warlocks aren't tanks, so you would rarely want to teleport and take the blow aimed at your bound companion. This warlock offers no benefits from being in melee, so they will likely be a back liner. This means not only are they less likely to be attacked, but when they use this ability to teleport say, their barbarian friend, and swap places, they are going to end up on the frontline and the barbarian ends up in the back. And, actually, that is a dangerous consideration. Let us say a single enemy charges the warlock and hits them, but the barbarian is in melee with three enemies who haven't gone yet. Tactically, you do not want to use this ability. Because it puts both characters out of position and is likely to cause your warlock to take more damage.
It can be fun and useful, but it is niche, which is why I think they get two abilities at level 10. This wish is just not terribly useful, in general. But, it is one of only two improvements to this binding, which is their only level 1 ability.
So, by level 10, the most you get out of this subclass in general, is the ability to grant a single ally fire resistance for an hour. Which, just saves someone a Protection From Energy spell slot. It just, isn't great.
dnd.wizards.com
