There are few reasons:

1. Forge is outdated. (14.23.5.2838).
   • Many projects for 1.12.2 used at least 14.23.5.2847.
2. Unable to fetch any of dependencies due to dead Maven repository links.
3. Probably outdated MCP mappings.

Dependences

AppleCore

The http://www.ryanliptak.com/maven/) gives 404. And seems there is no official maven anymore. Seems like author canceled development of his mod.

IC2 Experimental

The http://maven.ic2.player.to/) ded too.
But we have https://maven2.ic2.player.to/net/industrial-craft/ that still fighting.

RebornCore / TechReborn

The link http://maven.modmuss50.me/ is present, but seems there is no binaries for corresponding mods.