It’s widely common knowledge that airlines sell more seats than available in the airplane.
Maybe it’s because sometimes in the airport you hear the request for volunteers that are available to take a later flight (happened to me last year in Copenhagen) or because it’s frequent enough that it happened to a lot of people.

What is less common knowledge is that it might happen with hotels too.

I was in London 3 days ago and after a long day of traveling and business meetings I reached my booked hotel (Holiday Inn Express Park Royal) at 11pm.
I was warmly greeted and told the news about my missing room; I was then offered something to drink and invited to wait for the taxi that would bring me to a hotel with an available room with the reassurance that the complimentary taxi would be made available to me also the following morning to bring me where I needed to go.

The taxi arrived and after about 15 minutes I reached my new hotel (Holiday Inn Express Brentford Lock).
The clerk told me that the next morning there was no issue for transportation in the morning as a bus stop was near the hotel and would make me able to reach a tube station: no reference to the complimentary taxi.
I was very tired and simply went to my room to get some rest without arguing.

In the morning a different clerk mentioned the taxi (good move) but also told me that it would take 15 minutes for the taxi to arrive at the hotel and that using the bus would have worked fine and without additional cost for me as I have an Oyster card.
Unfortunately the part about the additional cost was not true (bad move): it costed me extra £ on top of the tube ticket. And clearly the hotel change costed me extra time (more train stops as I moved from zone 2 to zone 3 and a dozen bus stops not needed in the booked one) and discomfort.

No discount or complimentary benefit (WiFi, drink from the minibar) was offered to me.
I’ll think twice before booking again with Holiday Inn and I suggest that you do the same.