Image CC0 public domain
Twitter is a conversation tool and is often the place where people share personal information and their interests or positions on current issues. Scientists are also human beings and citizens, and their tweets are not necessarily based on their research work.
It is also a way to promote and share expertise or generate academic outreach. In that space, the debate between experts can take place informally (rather than writing lengthy article responses).
This does not mean that it is the place for the actual publication of research. Usually, academics on Twitter will summarise their research there but direct to a different source (academic publication, preprint, blog or other) which would preferably be used for citations.
Who's who on science Twitter and who counts? (2017, April 28). Absolutely Maybe.
Even the most notable tweets are fairly uninteresting for any academic writing usage:
There are still cases where Twitter is an appropriate primary (not secondary) source:
The APA style includes rules if you ever need to cite a single tweet in your work: https://blog.apastyle.org/apastyle/twitter/