ltspice: simple nmos circuit
You expected Amps instead of the mAmps you get.

I am quite sure that this has to do with the model used for the NMOS. You very likely didn't select a specific model nor did you specify a certain W/L. So LTSpice uses a default model which cannot conduct much current as it is likely more suited to model a small signal NMOS. It is somewhat similar to an NMOS you'd find inside an IC: quite small and for small currents only.

What happens now is that the NMOS determines the current and since it has a limited W/L it will not conduct much current.

What you need is a "really big" NMOS, with a very large W/L, one that is intended for switching high currents.

There is a library with discrete components in LTSpice. You need to see what is available there, then look in the datasheet of that MOSFET (type the model number in Google) and see what its maximum Drain current is.

After some Googling I found that maybe the IRF7401 is available in LTSpice, if it is there try it. It has an Rds_on of 0.022 ohm so that should work.