https://www.congress.gov/bill/115th-congress/house-bill/1/co...
I think the purpose of the change was to "increase revenue":
> Requiring that certain research or experimental expenditures be amortized over a five-year period or longer, starting in 2023, would increase revenues by $109 billion over the period from 2023 to 2027.
https://www.congress.gov/congressional-report/115th-congress...