The reason is, people do no want to see their effort reset to zero.
Considering how much I love this game, this is my very first eyebrow raise at the way the game is.
I'll wait to judge, but if a brand new Suros with zero Xp is now worth the same as a fully upgraded one (18 energies sunk) to Xur I will be annoyed to the nth.
To just wipe progress screams Grundy grind grind.
But the main reason? Why should I bother leveling multiple exotics before house of wolves? This move shows that their changes will make previous progress obsolete,therefore the grind just got tenfold less appealing.
There will be very little content that will require more than a 300 damage weapon.
Pick the few that you actually use and grind them out. For me, ghallahorn, icebreaker, possibly suros for new IB, and the new and improved thorn will be on my list.
Seeing as the hard raid won't be available till January you have plenty of time to get those few weapons of choice up to par.
Also, is it ]confirmed that you can use a shard on a completely un-leveled weapon to get its base damage up or is that just speculation?