Here are some reasons:

Pro:

- Red dwarfs are by far the most common type of star in the Milky Way, at least in the neighbourhood of the Sun

- Red dwarfs exist for a long time (longer than ten billion years) which gives life a long time to spring into existence (or start via panspermia) and evolve

- Planets in the habitable zone of a red dwarf are tidally locked ("eyeball planets") due to their small distance to the star

So there is very likely to be a huge number of these types of planets with stable conditions over a long period of time.

Con:

Flares by the red dwarfs (which are not so rare) could destroy life on these planets