There would not be a logistical need to cancel fireworks as the new platform will be constructed in a different location north of the existing platform. It would not make sense to destroy one platform before the other is built as one platform needs to be in place in the event of construction setbacks.
With the existing platform in place and functional, safety and cost-saving measures are two clear reasons why Disneyland would stop the displays. Safety is already addressed as construction crews in the future Star Wars Land footprint and the 60th Celebration fireworks are co-existing nicely. Maybe exposed building materials would be a fire risk, but IDK, that reasoning is a little dodgy since construction will continue to go on for the next 18-24 months and trees have always been in the current fallout zone.
That leaves money. If this were the case, budget cutbacks would most likely affect Disneyland Forever, not the special event fireworks. Disney would lose more in attendance and revenue if they stopped the Halloween or the Christmas fireworks than if they canceled weekend displays in February...March... Attendees have an expectation to see fireworks at Christmas and during the Halloween events, but not so much during the off-season months.
Yes, I am completely speculating, but I haven't seen any credible source to prove why they would purposely undercut the busiest attendance season of the year.