Each attempts balance (which can be derailed by chance card draws, opponent attacks, and other factors) although they all play differently
Its a relatively straightforward formula: Market value = rarity + artwork + popularity(of the Pokemon)
This often also involves them retreating an active Pokmon with enough Energy and HP to trade a couple hits to put in a weak Basic just to stall for time without any consideration for the player's point total, and immediately losing because they did that while the player was on 2 points
Cards like Past in Flames, Seize the Storm, Summons of Saruman, and Isengard Unleashed were already going into the deck anyway, so why not add some more options with Deep Analysis, Memory Deluge, and Reckless Charge
This will allow you to fetch every artifact out of your deck into play
If you need more bodies, youll make a token, if you need more cards wellyoull give up a rat or something to get it, and if youve got a good board state, you can give your whole board menace to go after your opponent