Why does the Gemara give outlandish explanations for Mishnayos? Part 2

Daf Yomi (Bava Basra 19-20) has a great example of this. The Gemara discusses barriers that shield from Tumah and Shmuel makes a statement that anything that will be removed (is only there temporarily) is not considered a barrier. The Gemara then proceeds to ask a series of questions from Tannaic sources that seem to say that various things that are only there temporarily do shield from Tumah. The Gemara then goes through them one by one and gives one outlandish answer after another. here are the questions and here are the answers:

1. The Mishnah states that a box full of straw or a jug full of dried figs blocks tumah even if the box or jug is removed. However, figs/straw is something that will be removed (by an animal eating it or for other uses). The gemara now gives a list of qualifications that grow more outlandish as to to why the straw will not be removed:
1. The straw is spoiled. 
2. The straw has thorns as well so it's not fit to make mud
3. The straw is wet. 
2. A Baraisa states that the following block Tumah, grass that was detached and placed in a window, or grew there by itself; rags smaller than three fingers by three fingers; a dangling limb or flesh of an animal; a bird that rested there; a Nochri who sat there, a (i.e. stillborn) baby born in the eighth month; salt; earthenware Kelim; and a Sefer Torah. The Gemara then proceeds to ask questions on each one that it is only there temporarily and again the Gemara gives outlandish qualifications dor each thing to explain why it is not there temporarily. 
1. Grass 
1. The grass is poisonous. 
2. The wall is ruined (so the grass will not destory it)
3. The grass is 3 tefachim from the wall and does not harm the wall but bends into the window
2. Rags
1. The material is too thick to be used for a patch
2. It's sackcloth which is rough and would scratch the skin. 
3. It's not sackcloth, it's just rough like sacklocth
3. Dangling limb of an animal
1. The animal is tied up and can't move. 
2. It's a non-kosher animal. 
3. It's a weak animal. 
4. Bird
1. The bird is tied down. 
2. It's a non-kosher bird. 
3. It's a Kalanisa (a very lean bird). 
4. It's not really a kalanisa, it's just lean like a kalanisa. 
5. A non-Jew
1. He is tied up. 
2. He is a מצורע. 
3. He is a prisoner of the king
6. Salt
1. The salt is bitter. 
2. There are thorns in it. 
3. It's resting on earthernware so it does not harm the wall. 
7. Sefer Torah
1. It's worn out. 
2. It's burial will be in the window.

Lets think about this. The Baraisa gives a list of things that block tumah. The Baraisa in now shape or form qualified any of the things that block tumah, and yet the the Gemara proceeds to attach a long list of qualifications to the objects. How could anyone think for example that when the Baraisa wrote a bird it really meant, a tied up non-kosher Kalanisa like bird? 

Regarding the non-Jew, the Gemara is even more difficult. Does anyone believe that the King would put a prisoner in a window? Secondly, even a prisoner needs to go to the bathroom, stretch their legs, if so they will move out of the window and therefore should not block the tumah. 

In short, the Gemaras lengthy list of qualifications  when confronted with a simple list of unqualified things that block tumah is laughable. No one in their right mind would ever think to add these qualifications to a simple list (except of course the Gemara).