I see many reviews that are complete positive BS and are aimed at increasing the company's score, either to offset previous bad reviews, or because the company is hiring and wants to look good.
I would not say that this is "smart"... You might get people to accept offers but if the work environment is bad they'll leave so the end result is just to increase turnover and to trash the company's reputation (which will make hiring more difficult).
IMHO companies should forget about Glassdoor reviews and focus on the actual work environment. But of course the reality is that the Glassdoor score is a nice, simple metric that HR can boast about improving... so that's what happens, instead.