Question: Why are the catsharks smaller than the other sharks

Lesser-Spotted Catshark answered on 7 Nov 2017:

The lesser-spotted catshark is pretty small by shark standards, but it isn’t the smallest shark known to science. That honour currently goes to the dwarf lanternshark (Etmopterus perryi), a deep sea species which is usually less than 20 cm!

Sometimes evolution results in smaller body size because it takes less energy (less food) to maintain and can also make them easier to hide and avoid getting eaten themselves. Palaeontologists have also noticed that after major extinction events animals with smaller body sizes tended to be more likely to survive than larger ones. So being small can be a good thing!