What you purchase for your money, basically, is not "amps". You purchase value. If you value only 1 amp model of a pack so much that you're happy to pay $50, you buy the whole pack and you're happy. If the whole pack is a toy that equals $10 value for you (regardless of how many amp models you want to use), you don't buy the pack for $50. Asking to separate packs, you actually ask Line 6 to sell you the same value for 5x less money.
Line 6 decided to sell the new models only to those who value new stuff as $50 or more. It does make sense commercially, and Line 6 is a commercial organization, remember. They might consider a Christmas sale later in the year, though, when most amp-hungry users already paid their $$$, and making even $1 more would again make sense commercially.