Pumpkins =/ crafting material.
Pumpkins only use is to build/restock the pumpkin traps. Since (before this year) they came out every year it made sense that they'd be reused. Plus how else would players who had built them in previous years restock them? They'd run out of pumpkins eventually if they were tied to s specific year.
The special crafting material needed for holiday themed guns/gear during a holiday event (4th of July/Halloween/Zmas) has never been reused. Since the holiday themed weapons/gear could only be crafted during the event, there is no restocking issue/ So to prevent older players gaining an advantage they don't re-use the material.
This is why I recycle 99% of all the holiday components once the event is over, as it's just taking up space.