BGP advertises only the best path by default
BGP routers use a list of attributes to determine the best path. BGP routers will only advertise one single best path to their neighbors. When a better path is found, it replaces the current path. Advertising a path and replacing it with a new path is called an implicit withdraw.
Since we only advertise the best path, a lot of other possible paths are unknown to some of the routers. We call this path hiding.
This behavior can be changed using features such as BGP Multi-Path and BGP Additional Paths.
Links:
https://forum.networklessons.com/t/how-to-read-the-bgp-table/1234/59?u=lagapides
https://networklessons.com/bgp/bgp-attributes-and-path-selection
https://networklessons.com/bgp/bgp-multipath-load-sharing-ibgp-and-ebgp