Why not implement GHOST in bitcoin? GHOST can provide higher transaction throughput by minimized block interval, but community people seldom mention it. What's wrong with GHOST?
GHOST is outdated, the more relevant protocol based on recent research by Aviv Zohar et al is called "SPECTRE" - https://medium.com/@avivzohar/the-spectre-protocol-7dbbebb707b5, https://eprint.iacr.org/2016/1159.pdf.

It has many advantages over the traditional longest-chain rule of Bitcoin, but:


It requires a hard fork, something which has never been done intentionally in Bitcoin.
It is a huge departure from Bitcoin's protocol, and as such it will require extensive research and testing before it is even considered for inclusion in Bitcoin.


There are alts under development that are trying to implement SPECTRE, if it works well for them it can be a first step towards consideration in Bitcoin. You don't risk untested ideas on a $100B production system.