Partial mash question

When doing a small partial mash, why do the grains have to be in a bag?
Can’t they just be in my smaller pot and when it is done I could pour the wort thru a strainer into my larger pot?

You could certainly do that. I think the bag is just simplification and acts as a false bottom of sorts. Are you planning to sparge? If so that might be a better option for you.

I had not planned to sparge. I may be wrong but I figured that if I had plenty of water in the kettle that this would remove almost all of flavor from the grains.

If you go with your plan simply save some (1/2 -1 gal) of the strike water, heat it to 170° and pour it over your grains in the strainer.