In case of tug of war the more people participate the more strength they represent. And in case of muscles - the longer it is, the greater the number of myosin heads bind to actin when muscles contract. So why doesn't length matter?
Since I've found multiple answers that compare muscles to ropes, let me comment on why those explanations don't work for me. Ropes don't have "muscle" strength, they have tensile strength. So this analogy can only compare tensile muscle strength to tensile rope strength.
In the end I'm pretty sure I'll find out that tensile strength constraints the muscle strength. And that's probably going to be the reason why muscle strength doesn't grow with length - something does not allow it, otherwise it would get damaged.
But I'd like find out what exactly prevents further contraction. Is it mechanical receptors on the muscle cell which block deploarization? Mechanical receptors in tendons which send nervous signals (but then - do tendons get thicker in proportion with the muscle)? Something else?