It is done because Pokemon booster packs are always packed with cards in a specific order, and the rarest card is often the fourth card from the bottom
If you're just looking to get into the game with friends, this will give you the most value per dollar
Therefore, distributing the creatures into a curve with the hump at three and four mana would look like this: The reason you want to do this is because it provides you with solid chances to hit your two-, three-, and four-drops
Birthing Pod and cards like it are fun to build around, and ask you to incorporate a chain of creatures in your deck so you can work towards gradually more and more expensive creatures
You can check current market prices for your Silver Tempest cards using our free Pokemon card price calculator
UR08 Stomping Giant Playing up the trope of giants liking to crush people underfoot