Posting on old threads (if the thread is, let's say, more than a year or two old) is not recommended.
In many instances, the information in the thread is no longer relevant or correct. eBay policies change; what was true or valid may no longer be true or valid.
The thread may have been specific to one particular enquiry; the enquiry may have involved quite a discussion. Posting in the thread years later revives a long-done-with discussion – to no purpose. It is best for people to start a new thread with their specific enquiry, so that responders do not find themselves having to scroll through a tortuous discussion that has nothing to do with the new enquiry.