I cannot speak to the intent of the authors too much, but the obvious inspiration does something similar, and there could be a few reasons for it.
Marvel's TSR system in fact does a larger leap at an arguably lower scale, jumping from 1 (or 2 pending your edition of choice) to 10 tons going from Remarkable to Incredible.
A plausible reason for this is because there is simply not a lot of value to be had in breaking up that category much. There are things between that weight, but going from 3 to 10 tons is the difference between many commercial pickup trucks, to lighter-end semi-trucks or tanks. In a superheroic context there MAY occasionally be need for things between that benchmark, but I can scarcely think of many situations that would come up frequently where that hair needs to be split precisely.
Besides, the ability to lift is a wildly overstated value in many of these systems, it's almost a ribbon given to your damage output, that can give combat-focused characters something else to do in a rescue or feat-driven scenario.
What if we removed the current level 1 value (50 lbs), shunted each value up to 30 tons down one place and added a 70 tons value?
I know this change would mess with the 1/3 pattern of the ton levels but there are a lot of characters throughout the histories of several superhero universes (including the Invincible one) who fall in the 60 - 80 range. The limits of a 12-point level system mean that every one must count... surely there will be many more characters and protagonists around the 70 ton range than the 50 lbs one, who will need stats in game sessions?
Personally, I think the suggestion to "shift up" the strength scale is bad, because then you can never actually have a characterized pipsqueak, everyone is lifting at least as much as an adult person should, reliably, which sort of undermines player agency in a way. The ability to be bad at things is pretty important.
Another problem is that the highest Strength level 12 (1000 tons) does not reflect the highest Strengths in the comics or TV series. Omni Man can lift billions of tons. He moved an asteroid the size of Texas and lifted a mountain with one hand. I have no idea how this works in the game as currently written.
The book already addresses this for you.
"This assumes simply lifting something off the ground, and requires no dice roll. Lifts under harder circumstances generally require a STRENGTH roll."
Maybe a + at the end of 1k tons would illustrate to you better the intent, but usually the reason such systems stop giving you bigger and bigger weights to lift, is because there's simply not much point after a while. But also if one could simply CREATE a context under which a character is casually doing villain-level lifting feats (Omniman was an antagonist gang) then there's really no reason for teamwork. Overall your issue kind of seems to be at odds with the premise of games like this, because several heroes should have to collaborate to approximate a high-level strength feat like that (it also ignores that in-space lifting feats would inherently calculate differently and that was more a cancellation of velocity and momentum than anything, still impressive).
But on the topic, I think you're kind of missing the fiction for the specifics of scaling. Possibly there may be basis for a power that ups a character's lifting strength, but simply being able to stat invest into soloing certain rescue scenarios that should be a team endeavor for PCs seems a little bit obtuse, to me.
Too much homebrewing... Must... Eat... Klondike bar....