It's not so simple as the character limit in mysql, the database server that the forum presumably uses, is 65,535 bytes for a VARCHAR:
https://dev.mysql.com/doc/refman/5.7/en/char.htmlFixing this would mean some major changes to the forums software, which likely won't happen in this software, but the new forum software that is being developed uses a different database server which may not have this limit. So something like you propose is much easier to do with the new forum software.
Yes, it's a technical limitation. Epochtalk doesn't have the same limitation, though IIRC as of now there's a soft 64k
character limit (rather than byte limit), since it seems prudent to have some limit.