They are really good if your city has fucked up roads. Potholes, curbs, tram lines (or light rail) that are embedded in the road, even some older syle storm drains have slots wide enough to swallow bike tires that are over an inch wide. And the bike lanes are usually added to already worn roads or by storm drains, some old-style.

Fat tires are also great for sand and loose gravel, which is present in the city I live in. Fat tires are also significantly more stable at very low speeds, which is good around pedestrians (eg, rolling slowly through crowded boardwalks where there are no bike lanes- only stroads).

For an ebike, the rolling resistance is a relatively small tradeoff since the motor will overpower it. I don't really have a problem even with it turned off, though, as leg power is fine too. I primarily use the motor for the ultra steep hills here. Because riding up a long 18%+ grade sucks. (And motor power for dangerous road situations where keeping up with cars is mandatory, such as neighborhood bridge crossings without any bike lanes)