There are several reasons for this, including the fact that they were the first to be released and therefore more difficult to find and collect, as well as the fact that they were more popular in their day than many of today's most valuable Pokemon cards (which have only come into existence within the past several years)
Doubling power exponentially is really scary in the right build
Leonin Arbiter [Cat]: Another great Death and Taxes cat
Common: The easiest cards to find are known as "Common." A round black dot in the bottom right corner helps distinguish them from other varieties
Commander - also known as Elder Dragon Highlander, or EDH - is generally considered the most popular format in MTG
And finally, and most importantly, I reanimate both the Valkyrie and Forge, Neverwinter Charlatan with Grusilda, Monster Masher, and the entering creature's backup triggers