I guess they do it for getting recommendations of their own publications. The problem is that some universities use ResearchGate metrics for the evaluation of their members. This encourages abuse and fraud, because some of these numbers (especially the Research Interest Score) can relatively easily be manipulated.
It is better you publish them here publicly. The method that I use.
When you speak with reliable references in sciences, it is acceptable and appreciable.
We are witnessing new forms of frauds in Science Social Media such as RG. So we have to be open and frank to discourage them.
Besides the case you mentioned, there are many other forms,
Such as those who recommend each others answers all the time, those who see others superior, therefore they recommend everything, the superior adds (pubs, comments, questions, discussions...), some others use the place and country of living to impress others (these when add answers get false recognitions, even when they are completely wrong) also there are some people that ask questions and start discussions like a flood, every day or week or so on. Some others ask baseless questions, some others in the frame of a discussion or a question advertise or rather propaganda for others, for example for predatory publishers/journals, there are too many other forms...
In all that I have found out I have been open and frank to them
To have a flavor, and encourage you, I invite you to see my comments to these:
4136 reads and 26 recommendations in my main article."
Don't worry, act healthily, be honest, be frank but polite, and stick to universal scientific norms, certainly you receive positive recognition and appreciation from community of scientists all over the world.