NASA has technology, MOXIE, to convert CO2 into oxygen. Why isn't the technology utilized to reduce greenhouse gas emissions in Earth's atmosphere?

You will need about 100 kcal to convert 44g of CO2 into oxygen and carbon.
The energy will come from combustion of carbon to CO2, most likely.

Same as the reason why few distill saltwater in order to get freshwater...the insane cost, namely through power consumption.
Moxie is capable of producing up to 10g of oxygen an hour with a power consumption of 300w
NASA has admitted that if successful a larger one could be sent which would produce 2kgs of oxygen an hour but would require a power plant generating up to 30kW.

It's much easier and cheaper just avoid the emissions.

We're working on it. Intelligent landscaping is a start. Artificial 'leaves' are also being used to filter CO2.

But like like recycling, it doesn't work unless you start with prevention.

Perhaps you haven't heard of sovereign nations on Earth. You can't just release something into the the planet's atmosphere without worldwide cooperation and agreement.

Maybe it isn’t practical in some way. Or nobody has the cash to build it on a scale that would make a difference