Have you ever actually read the contract constituting an airline ticket?
Here is the contract:
https://www.united.com/web/en-US/content/contract-of-carriage.aspx
All of UA’s flights are subject to overbooking which could result in UA’s inability to provide previously confirmed reserved space for a given flight or for the class of service reserved. In that event, UA’s obligation to the Passenger is governed by Rule 25.
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Rule 25 Denied Boarding Compensation
Denied Boarding (U.S.A./Canadian Flight Origin) - When there is an Oversold UA flight that originates in the U.S.A. or Canada, the following provisions apply:
Request for Volunteers
UA will request Passengers who are willing to relinquish their confirmed reserved space in exchange for compensation in an amount determined by UA (including but not limited to check or an electronic travel certificate). The travel certificate will be valid only for travel on UA or designated Codeshare partners for one year from the date of issue and will have no refund value. If a Passenger is asked to volunteer, UA will not later deny boarding to that Passenger involuntarily unless that Passenger was informed at the time he was asked to volunteer that there was a possibility of being denied boarding involuntarily and of the amount of compensation to which he/she would have been entitled in that event. The request for volunteers and the selection of such person to be denied space will be in a manner determined solely by UA.
Boarding Priorities - If a flight is Oversold, no one may be denied boarding against his/her will until UA or other carrier personnel first ask for volunteers who will give up their reservations willingly in exchange for compensation as determined by UA. If there are not enough volunteers, other Passengers may be denied boarding involuntarily in accordance with UA’s boarding priority:
Passengers who are Qualified Individuals with Disabilities, unaccompanied minors under the age of 18 years, or minors between the ages of 5 to 15 years who use the unaccompanied minor service, will be the last to be involuntarily denied boarding if it is determined by UA that such denial would constitute a hardship.
The priority of all other confirmed passengers may be determined based on a passenger’s fare class, itinerary, status of frequent flyer program membership, and the time in which the passenger presents him/herself for check-in without advanced seat assignment.
Transportation for Passengers Denied Boarding - When UA is unable to provide previously confirmed space due to an Oversold flight, UA will provide transportation to such Passengers who have been denied boarding whether voluntarily or involuntarily in accordance with the provisions below.
UA will transport the Passenger on its own flight to the Destination without Stopover on its next flight on which space is available at no additional cost to the Passenger, regardless of class of service.
If space is available on another Carrier’s flight regardless of class of service, such flights may be used upon United’s sole discretion and the Passenger’s request at no additional cost to the Passenger only if such flight provides an earlier arrival than the UA flight offered in 3) a) above.
Compensation for Passengers Denied Boarding Involuntarily
For passengers traveling in interstate transportation between points within the United States, subject to the EXCEPTIONS in section d) below, UA shall pay compensation to Passengers denied boarding involuntarily from an Oversold Flight at the rate of 200% of the fare to the Passenger’s first Stopover or, if none, Destination, with a maximum of 675 USD if UA offers Alternate Transportation that, at the time the arrangement is made, is planned to arrive at the Passenger’s Destination or first Stopover more than one hour but less than two hours after the planned arrival time of the Passenger’s original flight. If UA offers Alternate Transportation that, at the time the arrangement is made, is planned to arrive at the Passenger’s Destination or first Stopover more than two hours after the planned arrival time of the Passenger’s original flight, UA shall pay compensation to Passengers denied boarding involuntarily from an Oversold Flight at the rate of 400% of the fare to the Passenger’s first Stopover or, if none, Destination with a maximum of 1350 USD.
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