ECMO is not sustainable for long. The extra mechanical stress on the platelets and all the precautions you have to take against blood clots forming on any off the artificial surfaces are rather damaging. And since it is an expensive, short-term-only intervention there is no need for it to be particularly mobile. For the few days to weeks you are on ECMO while quite seriously ill, the ICU is the best place for you.

Ventilation on the other hand doesn't interact with your blood, but only has to handle air, which doesn't get damaged by the vent. So it is not impossible to be on a vent for decades. Being locked in the ICU for decades would not be good and luckily is not necessary.