In many fonts, all numbers are the same width, so they line up nicely.
The TPT font isn't like this, so, for example, as the FPS changes, its width in the HUD slightly changes whenever there's a "1" in the number, even if the amount of digits says the same.
"Most fonts" aren't like this, the ones you're mentioning are monospace fonts.
Regarding to the post, this is just an aesthetic decision, maybe the developers would rather stick to the classic non monospace font. Monospace fonts also waste space when there's a narrow character, so.. Its up to them