Stupid UK tax system – Ch.6 TRADING PROFIT – BASIS PERIODS

Can someone explain me the logic behind basis periods?

Example 4
________
John commenced trading on 1 December 2020 and prepared accounts to 31 May 2022 in which period he made an adjusted trading profit of £54,000.
The adjusted trading profit for the accounting year ended 31 May 2023 is £48,000.
Compute the assessments for the relevant tax years of assessment for the information provided and calculate the amount of overlap profit arising and state what will happen to the overlap profit.
_______
Answer
2020/2021 —- 4/18 * 54,000 = 12,000
2021/2022 —- 12/18 * 54,000 = 36,000
2022/2023 —- 12/18 * 54,000 = 36,000
2023/2024 —- 48,000
etc….
Overlap profit = 30,000

I mean, I understand how everything was calculated. But why??? Why do you need to re-calculate the same trading profit 3 years! that’s so stupid.
Why can’t you just calculate everything like this:
So from 1 December 2020 till 31 May 2022 we have 18 months.
2020/2021 1December2020 – 31 May 2021 = 6 months >>> 6/18*54,000
2021/2022 12 months >>> 12/18*54,000
2022/2023 12 months >>> 0
2023/2024 12 months >>> 48,000
So in this case there is no any overlap profit. If the Company anyway at some point will have the same acc.date for the tax calc as they have it for the acc.purpose, why don’t we just start taking the same period from the second year?

What’s the point of this overlap profit and 2 years taking the tax date (5 April), and then suddenly the third year bingo! we take the same YE for the tax purpose as we do it for the acc purpose.