There is an inherent conflict of interest between travel review sites and the targets of those reviews. Travel review sites depend upon those being reviewed for their revenue. So, when those who pay the site ask that a negative review be removed, well, some do succumb. TripAdvisor will delete negative reviews on, for example, facilities, if the hotel can show that the facilities have been updated or repaired. TripAdvisor does notify the poster that the review is being taken down.
Some companies pay people to write reviews. The online review sites have caught on and are now requesting proof of a stay or meal, depending on hotel or dining reservations. Sometimes the threat of suit causes the removal.
In short, you may not be getting either the most-up-to-date information or authentic reviews. Who knows? However, be aware when using travel sites — some are gaming that system.