You need a good BMS too, the issues mostly arises from cells being overcharged because single cells are broken and not taking a charge anymore.
With NiCad and NiMH cells the batteries would just get warm and eventually the charger would hit a time or temperature limit.
With Lithium cells the charger or BMS have to detect this condition and stop the charge.
Most lithium cells will start breaking down very quickly once they are being overcharged, which is often resulting in fires.
On the other hand, fires of cars and such are also not really uncommon but often happen outside and cars also do not scale well in high density areas but eBikes eventually will.
What worsens the whole situation is the inconsequential regulation or the lack there of, of eBikes which prevents bigger players from entering the market and creating a common quality level.
Looking at Europe and Japan far over 90% of the eBikes are big brands which could never tolerate such failures in their product lines.