As Bob wrote already, this is a religuous topic Nevertheless I'll try to summarice the facts:
All of HP's pocket calculators up to and including the famous HP-41C had the arithmetic operators on the left below ENTER. The Voyagers had to put them on the right for obvious reasons. With the Pioneers, they staid on the right - but ENTER remained on the left. So much about HP's logical development.
There was a very extensive discussion of this topic on the forum of MoHPC in 2012 IIRC, followed by a poll. After all, many people agreed on ENTER and the 4 operators should be in the same column (for various reasons). And the poll resulted in our decision (we, the developers) to place the 4 operators on the left, backed by a majority of votes IIRC.
So, now they are there.
There is, however, a medicine for those who would rather die than accept the 4 operators there: you're free to reassign each and every key and function of the 43S except USR. Hope this helps.