For one thing, the filesystem layout of most relational databases is such that storing large blocks of arbitrary text or data can slow down the system. Since data is usually stored by row, when doing searches the database now has to skip over variable-length text fields even when looking for unrelated fields.
Second, putting everything in one table makes it much harder to add to the data model later on, if you need more data for each thread_id, for instance.
Designing database schemas well requires some education. You should start with http://en.wikipedia.org/wiki/Database_normalization. Be sure to understand third-normal form.
