The “modern electronics” you mentioned are very low-power devices in the range of things you can power from a household socket. They’re also low-voltage DC, which means that no matter what voltage/frequency you can get from the wall it is being converted, and converting AC to DC is electrically very simple. The difference in circuitry between converting from 110V or 220V is just a transformer with a center tap, and the frequency doesn’t matter at all since DC is 0Hz anyway.

With high-power devices, pretty much anything with a motor or a heating element, the device is designed to match the voltage and frequency available in the region they’re going to be used. An AC motor’s speed depends on the frequency of the power supplied to it, and a heating element depends on voltage, which is why electric kettles and ranges boil water much more quickly in 220V regions. Travel adapters are basically just a transformer, which changes the voltage but not the frequency. The difference between 50Hz and 60Hz isn’t that big so most motors will still run but with impaired performance and maybe timing issues, but others will fail in spectacular and dangerous ways. Supplying a heating element with the wrong voltage will make it either not heat up, or heat up too much and start a fire. The different plug types ensure that you don’t plug in a high power device to power it’s not designed for.

If we were going to standardize on one plug type, we would also have to standardize on one power signal. Ignoring the political issues, that would mean that any region that doesn’t already use that standard signal would have to immediately retool all of their power plants, their entire transmission system, every industrial facility, and adapt or replace every AC household appliance. And there’s not really any good reason to do it, other than convenience.