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GHOST is outdated, the more relevant protocol based on recent research by Aviv Zohar et al is called "SPECTRE" - https://medium.com/@avivzohar/the-spectre-protocol-7dbbebb707b5,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.
One thing to note also is that even ethereum is not using GHOST and I dont see any coin using some sort of ghost or phantom protocol at this point, so yeah its hard to expect bitcoin will jump to it before it is tested elsewhere.
We are using a modified version of Ghost at Hycon. The original plan was to move forward with Spectre, but as yet there are some unsolved issues, particularly around selfish mining and efficient resolution of superposition states at the tips of the DAG. Ghost is useful when the block time is shorter and orphan events are more common. In the case of bitcoin, these days orphan events are rare, so unless it was decided to reduce the block time it is unnecessary.