All hiring managers will have to play their cards right, meaning they have to be seen as showing keen interest. Whether or not it is genuine or even relative it can be different.
For example, if your interview was at 10am and you were the first and did well. Of course the Hiring Manager would be keen. But by 4pm, another candidate comes in, way better. Of course the Hiring manager will be even more keener then. Then later that week got an even better candidate comes in.

By that time, the hiring manager has to weigh all the options and probably push for the candidate of choice to HR to follow-up on first.

To be really frank, don't put your hopes up high the moment there is radio silence.

As a hiring manager, "On-hold" really means "I have found someone better, if I can't get that person whether it is the pay/job preference or not then I will go through my on-hold list".

That is what on-hold really means.

If they told you straight you might not be interested. Means the employer would also lose more candidates which would extend out the hiring process as well.

If an employer still constantly reviewing their applicants, it means also that the bar is set quite high for a particular role. Either that or the role itself is changing (e.g. budget cuts, have to lower job grade, hiring freeze)