Retired

Somtimes kits are improved upon and the old ones are retired.

Sometimes components go obsolete, resulting in the kit they were used in being retired.

Sometimes there is no longer enough interest in a kit to keep it in stock, so it is retired.

Sometimes unforseen bugs are found meaning the kit has to be retired.

Sometimes a kit is made for a specific purpose or a limited run and is then retired.

Whatever the reason for retiring a kit, the documentation may still be useful to others in the future.  If you bought your kit a while ago and have only just got around to assembling it, the documentation is probably here.