>> 1. Go increases in popularity.
Lots of people rush into the market with the newly learned Go skills and the salaries take a dive.
>> 2. Go decreases in popularity. Many many projects still exist that are written in Go.
These need to be maintained. Maintenance jobs pay poorly and do not advance one's skill set, leaving one with the outdated skills after a while. New shiny things are developed in new languages and those who quickly learn them before everybody else get to earn some good money.
Specialization gives you an edge... for a brief while until this skill becomes a commodity and is eventually outsourced.
Lesson to take: focus on some skill which cannot be easily learned by a vast army of outsourced workers. Everyone can learn some Java or Go or whatever. Not everybody can run a consultancy. Not everybody can talk to humans and translate their needs into software solutions. Not everybody can found a company. These are the skills that provide the highest ROI in the long run.