South Australia has run into this problem and implemented a solution.

When the solar exports in a section of the grid exceeds the local transformer's limits, a signal is sent to all of the inverters in that section to limit the export rate. The same signal can be send to all solar inverters in South Australia if the entire grid has too much renewable energy.

This signal only limits the export to the grid, so the homeowner can always use their own solar power first. The permitted export is guaranteed to be between 1.5kW and 10kW per phase.

The was a minor oversight during implementation. Homeowners on wholesale pricing would often curtail or switch off their solar inverters if the prices went negative. If the grid operator sent a signal to reduce the export rate, it would override the homeowner's command and force a 1.5kW export during negative pricing (costing the homeowner to export). No-one considered that anyone might not want to export solar all of the time.

Then tell me why the mechanism to control production via the solar panels themselves hasn't been implemented?

Why would you want people to tell you things that are untrue?