‘They’ want them dumb, sick and/or easily manipulated - or under intense blackmail.
For the majority of congress the “professional” staffers do about 95% of the actual work. They write the bills behind the scenes, allocate funding, and make the quid pro quo trades that are the lifeblood of the swamp (and why it is so wealthy).
For this reason, many who are intimately familiar with the workings of congress understand where the real power lies and it is NOT with the representatives.