IIRC LinkedIn actually does tell you how many applicants have applied via their platform, but since it doesn't tell you 90% don't have the right to work in the country never mind meet the job spec in other requirements, it's not information that's particularly useful.
"We're the job board that forces you to jump through hoops to provide evidence of how active your hiring process is" isn't a sales pitch particularly likely to attract employers (in which case there's not much incentive for candidates to pay them either). And even if it did, it wouldn't replace Glassdoor' reviews - with all their inadequacies - for people that care more about whether the employer sounds better or worse than their current employer than whether they will get a job offer by the end of tomorrow.
"We're the job board that forces you to jump through hoops to provide evidence of how active your hiring process is" isn't a sales pitch particularly likely to attract employers (in which case there's not much incentive for candidates to pay them either). And even if it did, it wouldn't replace Glassdoor' reviews - with all their inadequacies - for people that care more about whether the employer sounds better or worse than their current employer than whether they will get a job offer by the end of tomorrow.