answer:It’s simpler to work in illustrator for this brush if you are averse to pen pressure. The reason for this is because the brushes in Photoshop are not mathematical, yet in illustrator they are [because illustrator works with vectors]. The problem is that Photoshop does not know when you will finish the stroke, therefore it does not know when to make the stroke wide, and thin again. Illustrator, on the other hand, knows when you finish the stroke and can adjust the stroke as soon as you finish making the stroke. It’s sort of like post processing – and that is possible because the lines [everything actually] in Illustrator are mathematical. Hope this helps you understand the “why”.