When a cell/row is selected, its first cell is focused and the sheet is scrolled to show it. If a long sheet is scrolled down/right to edit cells, this scroll top/left is very annoying and user unfriendly.
In these scenarios Excel focuses the topmost/leftmost currently visible cell, avoiding sheet scrolling.
NOTE: for rows reproduction select cell AX2, then click on the header of row 2 - sheet is scrolled to the left and cell A2 is focused.
Column C is selected, cell C1 is focused and the sheet is scrolled to top.
The used has to scroll down to the bottom row again to edit data at the bottom of the sheet.
Column C is selected. The currently visible topmost cell of column C is focused, without scrolling the sheet. Excel works that way