Why can’t I convert from Animism to Catholic

1a) The wealthier a province is, the more difficult it is to convert. Look at a correlation between the economic strength of a province, and that modifier. 1b) The "Local Missionary Strength" modifier is a natural feature of Sunni Islam, it reduces the effectiveness of your missionaries there by 2.5%, the stock strength of a missionary varies. You can see you bonuses and maluses on the religion tab.

You cannot remove the Local Missionary strength modifier from the Sunni faith outside of creating a mod for your game, so the only way you are going to even have a chance of converting Islamic provinces is with the Religious idea's "Divine Supremacy".

2) I would say the best way to convert Islamic provinces is to pour points into the Religious idea, and then starve them for wealth by supporting rebellions (which sap province wealth over time).

Besides stability, which you said you are keeping high, there are four main ways to improve conversions.

1. For converting large areas, your best weapon is the Religious idea group. Among its ideas are one giving +3% to conversions and one that gives an extra missionary. However, consider the opportunity cost - there are more valuable admin idea groups than Religious (I would usually rather have Innovative or Administrative ideas, for instance).

2. If you have the money (500 ducats) and the military strength to back it up, you can get an extra missionary by declaring yourself defender of the faith. You lose the title when you lose any war, so be careful.

3. Western nations also have many decisions which can strengthen missionaries by 1% each. Two of them (Act of Uniformity and Advancement of True Religion) cost nothing, while others reduce tolerance of heretics (i.e. Catholics and Reformed, for a Protestant nation), reduce taxes, or increase stability cost. If you don't want to go down the Religious ideas route, enacting some of these decisions can significantly speed up your conversion time.

4. Finally, if you are lucky and/or rich, you can hire an inquisitor advisor for +2% missionary strength.