Because they really are that good. I hate feats like this same as you, but yes: unless house ruled, everyone should always take them, always.
...
Here's another thought: HR it so that each expertise feat gives a +1/2/3 feat bonus to ALL attacks, rather than simply a single set of weapons / implements / whatever? I mean, I don't really like it, but at least this solution fixes the problem with needing multiple expertise feats. This way, you still have to pay the feat tax (bad), but you don't need to take multiple expertise feats regardless of your weapon choices (good).
Ok, I had a chance to read the new Essentials Expertise feats.
I don't see a need to change them at all for LEB.
Yes, they are potent and some players might see them as "should always take".
But, who cares? Let's take an example:
Light Blade Expertise
It's +1 to hit, +2 to hit at level 11, and +3 to hit at level 21. It's also +1 damage if the PC has Combat Advantage.
Weapon Focus is +1 damage, +2 damage at level 11, and +3 damage at level 21.
At LEB, the PC that takes Light Blade gains:
+1 to hit at levels 4, 11, 12, 13, 14, 21, 22, 23, and 24. 9 levels out of 26 and it takes two years to get to level 11. He also gains +1 damage when he has CA. This PC does better damage at level 4, might be slightly better at levels 11 through 14, and is probably slightly worse at levels 21 through 24.
The PC that takes Weapon Focus gains +1 damage immediately, +2 damage at level 11, and +3 damage at level 21. This means that this PC does better damage at levels 5 through 10, 15 through 20, probably levels 21 through 24, and definitely levels 25 through 30.
All in all, Weapon Focus is better at most levels.
Since the feat bonus from the free LEB Expertise does not stack with the feat bonus with the new Essentials feats, it means that the PC mostly gets the side benefit, plus he's +1 to hit at level 4 (and possibly levels 11 to 14 if he ever gets there).
That doesn't sound unbalanced, nor does it sound like it needs an LEB house rule to me. I know how I would vote is someone were to propose a +1 flat bonus to hit for the feat. Making the feat more potent than it already is doesn't make sense to me.