People have asked for all RXP off a NPC before too; it likely falls into the same typical response of "It's not something we're testing at current time; so we don't need people to suddenly have X or Y extra power they don't have on live. Lam is here for testing/trying stuff for the specific update and not for a free for all playground of trying out things beyond your normal level of gameplay."
The thing is, though, that people are going to use it that way, because its the only way to get that kind of sandbox functionality, and its a very useful function. The devs need to be pragmatic and just accept that inevitable reality.
If they want to get useful and actionable feedback from Lam, they need to make it more streamlined to draw up a sandbox character. Right now you can spend a good 30-60 minutes just going through all the manual processes to create the character you want to test, between transferring and reincarnating your Live characters, leveling them up, unlocking Destinies, assembling gear from all the various Loot Guy menus, grinding thousands of SXP with items one by one, shopping the Store for augments and extra stuff, etc.
If they made it faster and easier, then that's time you're not spending testing
your things, and more time you can spend testing
their things.
If they just left Lama open 24/7 as a sandbox server, then they'd get a
lot more focused feedback when a new preview hit.