setRequestUri is supposed to update the object returned by getUriInfo, not to make getUriInfo return a new object.

The javadoc for getUriInfo says:

The returned object contains "live" view of the request URI information in
a sense that any changes made to the request URI using one of the
setRequestUri(...) methods will be reflected in the previously
returned UriInfo instance.

— Source: https://jax-rs-spec.java.net/nonav/2.0/apidocs/javax/ws/rs/container/ContainerRequestContext.html#getUriInfo%28%29