OpenGL and DirectX are rasterisers. At the very lowest level they just move pixels into a memory buffer one at a time.
Things like Tempest in the arcades were vector games. You supplied a list of lines to the hardware and it drew them to the screen, not a memory buffer.
Flash was very clever when it first came out. At the very lowest level it had a 256 colour (byte per pixel) render buffer. All draws were converted into a list of horizontal lines. These lines were then kind of depth sorted until only the visible segments were actually drawn into the memory buffer.
This 256 colour array was then passed to the hardware in the most sensible way.
So to render a filled shape, they scale the control points by the camera, calculate every point on the curve, find top and bottom points, create left and right point lists, add horizontal lines between them. (it's a little more complicated than that as you can have multiple lists per glyph to handle peaks). Sort all glyph line lists by depth, create a draw list. Parse draw list to memory.
A hell of a lot of work.
Using vector fonts is more flexible than any form of bitmapped fonts, but is it worth it?
The amount of code required , and cpu cycles burned, to render a single glyph.... well it's prohibitive. Unless you really need it, the quality of the rendering just isn't worth the overheads.
Especially if you are working on mobile devices. You may have a 1920 by 1080 display, but it's a six inches big. Is it worthwhile having vector fonts?