> and that this is common folk knowledge among solar installers.

I think it's partially that people want to spend less money and undersize their inverter setup. The average end user non technical consumer (maybe a person buying an off grid PV system from an installer) may not fully understand what 1500W really is, and that something as boring as a $35 tiny space heater that sits on the floor can be a 1500W load.

People will be really surprised if you tell them that their tiny floor space heater uses the same amount of energy as charging twenty high performance laptops simultaneously.

It takes just a few high wattage single item electrical things to totally screw up the electrical load budget of a site, if somebody has something like a single 8000W rated inverter.

If you want to use electric space heaters and kettles and hairy dryers and hair curlers and such, along with the other regular daily load items of a house, you're looking at a setup with multiple 6000-8000W inverters in parallel with each other and synchronizing their output waveforms. Not many people want to spend the sort of money that'll get them 3 x 8000W inverters in parallel with each other all properly installed in an electrical room next to the PV stuff, breaker panels, etc.