because to implement that "other technologies" into space business takes a lot of time and money, so why don't we use the one that is available and is still good for the next 5-10 years time?
then after that, maybe the people at NASA will consider to use that "other technologies" you mentioned
I still find it amazing that in the 21st century we still use internal combustion propulsion systems for rocketry, when there other technologies are proven to be more efficient and less energy consuming.
