Most home solar installs are sized far above the steady draw of the house, who actually uses 5-6kW continuously during the peak solar production hours?
One house, no so much a problem. When most houses on a low voltage feed do this at the same time its like a reverse of the "normal" (previously designed for) situation of all the houses drawing 5-6kW at the same time.
So what used to be a normal: 240V high, 220V low fluctuation from no load to 100% load, becomes 260V high (-100% load) or worse.
Double the distribution conductance and cost (halve the resistance) ? yes that would eliminate the problem, but is quite expensive. The grid wasnt engineered for this flow, but slowly slowly it can be upgraded to meet the demands, just as it was slowly updated as people built in higher and higher density. Who should pay for that upgrade is the sticky question.