Probably it is a traditional behavior from Standard, but it has an economical issue. See the following picture:
(https://cdn.discordapp.com/attachments/623519850714890265/739780145463951400/unknown.png)
Diagonal ways cost as much as straight ways, although they have only 1/sqrt(2) length. I think that the way building costs (including the forge costs) must be proportional to the length.
I suspect the current behavior is the best we can get, at least without redesigning costs of junctions and crossings.
Very bored people that want to save some money could then abuse this by buildind very many short diagonal tracks in parallel, then connecting the straight direction and getting rid of the junctions in between those parallel tracks.
Thus, they had built a double tracked straight line at the cost of diagonal ways.
This is unfortunate. However, it is difficult to see any solution without a fundamental redesign of the code, since any given tile that is on a diagonal can be changed at a later time to be straight and vice versa without any rebuilding of the tile itself, so there is no reliable way of distinguishing which tiles are and are not diagonal at build time.