This is the way I understand the logic, right or wrong, I am sure someone will correct me.

Genrators, UPS, inverters and the like are designed for a specific application, which is why they are class 11 devices, not orginally designed to be connected to fixed electrical installation.

A class 11 devices doesnt have a floating neutral, it has 110 VAC on each leg, which reduces the voltage to make it a little safer for mobile use.

A floating neutral is a floating neutral in a 3 phase supply which creates an extremely dangerous situation, in the past neutral condustors have been stolen in sub station because the thief has learnt that they will not get electricuted if they cut it.

IF you are an electrician and been called out for a burning smell in a property, or burnt plug tops, ballasts and the like, you would have carried out tests and realised that the power had to be switched off asap, why because the voltage measured would in some cases be as high as 600-700 VAC