"prolly because they can’t control what the creator of an entry uses for the URL and they’ve got thousands of people doing so, most probably not aware that this can cause a problem”
They do have pretty exacting standards of what can be used as a subject title, and non-compliant titles are repaired. The URL is determined by the subject title.
The use of parentheses to disambiguate is a matter of policy.
For disambiguating specific topic pages by using an unambiguous article title, several options are available:
1. When there is another term (such as Pocket billiards instead of Pool) or more complete name (such as Delta rocket instead of Delta) that is equally clear and unambiguous, that should be used.
2. A disambiguating word or phrase can be added in parentheses. The word or phrase in parentheses should be:
* the generic class that includes the topic, as in Mercury (element), Seal (mammal); or
* the subject or context to which the topic applies, as in Union (set theory), Inflation (economics).
3. Rarely, an adjective describing the topic can be used, but it is usually better to rephrase such a title to avoid parentheses.
4. With place-names, if the disambiguating term is a higher-level administrative division, it is often separated using a comma instead of parentheses, as in Windsor, Berkshire. See Wikipedia:Naming conventions (settlements).
EDIT: FWIW (probably not much), I don’t agree that the solution is leave them out of URLs. The HTML standard for URLs is not new: if someone designs software that fails to recognise and interpret a compliant URL as a compliant URL, then they’ve written faulty software. Square brackets and less than/greater than are commonly used for tags in scripting, presumably because parentheses are such a common part of the language.