I'm confused. The requirement to amortize software engineer expenses was introduced in Trump's first term, but now he wants to revoke it in OBBBA? But only for 5 years?
Besides "kicking the can" to another administration, the 5 year thing is a hack to get budget legislation past the CBO.
The CBO calculates costs over 10 years, so if you introduce a tax cut that sunsets after 5 years it looks much less bad (for the deficit) than it really is. Then you hope that in 5 years some other legislation comes along to renew it for another 5 years...
It was passed in 2017 to go into effect in 2023. Trump now wants to suspend it until 2029. You may notice that in both cases it is being passed under a Republican-controlled executive but goes into effect under the next administration. This is the point.