Why a guest who found you on a booking site books elsewhere anyway

A booking site answers the standard case very well

Photographs, prices, availability and reviews are all handled better by a large listing than by most hotel websites, and competing on those is competing where you are weakest. What a listing cannot handle is the non-standard guest: the one travelling with a wheelchair, arriving at three in the morning, bringing a dog, needing two connecting rooms, or asking whether the quiet side of the building can be requested. That guest comes looking for you.

The switch happens at the point of an unanswered question

A guest who finds your own site and still cannot get their question answered does not telephone - they go back to the listing and book the standard room, or book the hotel next door that answered. The commission you paid on that booking was not lost to the listing's convenience; it was lost at a specific unanswered sentence on your own page, which is a thing you can find and fix.

Measure which questions arrive on your own site

The questions asked on your own site, as distinct from the ones that reach reception by telephone, are a direct readout of what your listing does not cover. Keep that log for a month and you have an ordered list of what to publish, ranked by how often it was the last thing somebody asked before leaving. This is far more actionable than a general instruction to improve the website.

Be honest about what the booking path actually is

If your own site cannot take a booking, say so and say what to do instead rather than implying it can. A guest who answers five questions and then discovers there is no way to complete the booking has been given a worse experience than one who was told at the start. And if the booking path does exist, the questions have to be answerable in the same place, at the same hour, or the guest leaves between the question and the form.