Nope, I don't know if there's any specific reasoning for why things work this way, but characters like Goliath/Giant-Man have their strength grow proportionally with their size while Ant-Man's strength is retained as he shrinks.

Personally (and I'm sorry that this is long and I picture Pym particles working in 4+ dimensional space, I really am, but it's how I visualize things actually working) I'd probably explain that away as something to do with how Pym particles function; canonically, when characters shrink, they're sending extra matter to the Kosmos Dimension (which, if you can try to visualize it as a sort of actual invisible set of spatial dimensions [not necessarily what is meant by Kosmos Dimension, considering the common usage of "dimension" like parallel universe, but I think it works] like left/right or down/up, can work pretty well for explaining this phenomenon in my head, though I might not explain what I mean in the best way here), so (since they can regrow to their exact previous size) I'd bet they keep some sort of connection to that matter (dimension-wise, think of it as the Pym particle user moving partially into the hidden Kosmos dimensions rather than losing matter, suddenly a lot less of them is in "normal" space and so their physical form gets smaller, but they still have all their mass) which maybe lets them still use all that mass. For the other side, when characters grow, they're taking matter out of the Kosmos dimension; this matter is not tied to the user, for the same reason I think the lost matter from shrinking would be (in this case, they have to be able to lose the extra matter and return perfectly to original size), but they can still use all of it to interact with this dimension because it's all been moved into our reality. Hard to come up with a continuation of the dimensional explanation here, but maybe in the same way a character can move in one extra direction to get smaller and hide mass in the Kosmos dimension, maybe they can also move the opposite direction to pull more of their full 4+ dimensional form into "real" space; this does screw up the "connected to"/"unconnected to" the lost/gained mass argument, but maybe there's a natural resting point for an object's position in this "size dimension" so to speak, and part of Pym particles' effect is to keep a shift in this position stable.

Wow that got longer and more complicated than I expected. I knew it was going to be tough to try to explain why I think Pym Particles function as they do, I just didn't really think it would be that long. I probably overthink these things just a tad bit (like visualizing extradimensional space).