why doesn t NASA send seeds to Mars?

The conditions on Mars are very different to Earth- the atmosphere is very thin and the gas concentrations are different, there is on surface water, and the temperature changes a lot, often getting very cold. If you just dumped seeds there, probably nothing at all would happen and they'd die.

It would be difficult to set up an environment where they could grow, and it would cost billions. NASA has better things to do with the money. Also generally the policy for space exploration is to minimise contamination of other parts of the solar system with living things, in case they damage the local environment or interfere with any other microbial life out there.

Those are good answers. Terrarium or green house is very costly and/or yields little science, but I'm sure NASA is looking for a good seed experiment, and some seeds that can grow plants in Antarctica in July, or any other month without adding lots of heat.

Elon Musk had planned to send an automated greenouse to Mars to show plants could grow there, but when he looked at the cost of launching it on any rocket available at the time, he was shocked at the price. So he started the company SpaceX instead. Now he plans to use SpaceX to send people to Mars as soon as he can. Which won't be very soon I think but maybe sooner that it would have been without SpaceX.

No water, little air, no bacteria in the soil, temperatures that make Antarctica look like a tropical paradise.

Have you noticed that on every mountain there's a tree line above which nothing grows? Mars is far less hospitable than the summit of Mt. Everest.

OK genius - if you can think of a type of seed that will germinate and grow with no soil, no liquid water, no oxygen, extremely low carbon dioxide and freezing temperatures just let us know.

No liquid water. Virtually no gaseous CO2. Freezing temperatures.

How would they Grow? NO Water.

Well, there wouldn't be any point - not enough warmth, not enough water, and for most plants, not even enough light...

They would die. There is no atmosphere, no free water and no soil.