I edited my post and quoted the source.
For one, that quote isn't a source, that's just common sense. Those "initial orders" are for sealed product, not opened product. For another, TPCi makes absolute ZERO if people spend $40 for a Shaymin EX. That $40 is going
entirely to the store selling the single, not TPCi. And the difference is that while they make an initial amount of money from selling the packs to vendors in the first place, they won't make more money off those packs without making another printing of them, and selling those newly printed ones to vendors. But vendors aren't selling the original packs, so why would they buy more stock that isn't moving? They wouldn't, so TPCi is printing less as demand for the packs drops, which means less money for them. Why aren't the original packs selling? Because any player who has their wits about them won't be buying packs in an attempt to get a Shaymin EX. They may buy at set launch in an attempt to get
everything from the set, but after the first week people don't do that anymore, and people aren't buying packs in the hopes of pulling one specific card because the odds are way too low.
Printing Shaymin EX in a tin would be making much more money for TPCi, as they'd have an additional source of income that wasn't there before. You can say that any promo in any tin would count as an additional source of income, and while that's true, the demand for Shaymin EX is so high and the supply so low that it's a goldmine waiting to happen.
That's exactly why TPCi doesn't want to release it as a promo! MewTwo is slashable but it's not a support Pokemon. I don't understand why you can't see what I'm saying. Of course those 3 EXs you mentioned got released as promos. They aren't as useful as Shaymin is. TPCi wants people to either spend $30-40 for each Shaymin by which many won't want to or buy crates of booster boxes to hope to pull a couple. Either way, TPCi makes money. Whether vendors open up crates and resells them or people buy a bunch of packs, it makes no difference. TPCi wins.
Yes, thanks for strengthening my point. Why was that entire deck (Big Basic Plasma) made cheap by those reprints? Maybe for the same reason that Shaymin EX as a tin promo makes sense? Supply vs Demand, while making TPCi more money? Those cards certainly aren't splashable, that couldn't have been the reason they were made as tin promos. It was very likely to get more copies of those cards out there to meet the growing demand for them. Shaymin EX is in a similar boat right now.
Shaymin EX also makes sense in a tin for the reasons Mewtwo EX makes sense, by being splashable. It's just as splashable as Mewtwo, if not more so, which makes it a great choice as a tin promo by being able to fit into the deck of anyone who buys the tin, meaning the tin has a wider appeal to players in general. Competitive players who wanted a Plasma deck, for example, would buy the Plasma tins. Casual players who wanted a Plasma deck, would buy the tins. Casual players who didn't want a Plasma deck
wouldn't buy the tins. In contrast, something splashable like Mewtwo EX or Shaymin EX, would have that third demographic buying the tins, because even if they didn't want to build, say, a psychic deck or a colorless deck, Mewtwo EX and Shaymin EX are very good and fit in their decks anyways.