Because state level Republicans have TOTAL control over redistricting in twice as many seats as the Democrats do, and an advantage in control in most of the remaining seats.

In 2012, despite having Obama on the ticket, the Democrats failed to regain the seats they lost in 2010. This failure was due to redistricting, which cemented the Republican advantage in the house. The democrats couldn't regain the speakership until 2019.

The same thing happened to them in 2002, when Hastert survived despite Bush being unpopular. Again, this was due to redistricting.

The state Republicans will create another Republican house through redistricting, and once again it will take the Democrats most of the decade to dig themselves out of the latest hole redistricting put them in.

This happened because they gave up on their goal of trying to compete for state houses. After 2012, the DNC and DCCC had made it their goal of not being in that situation again in 2020. They wanted to win 2020 at the state level. But Trump beating Clinton changed all that. It made them lose their fucking minds and forget their long term goal.

Because state level Republicans have TOTAL control over redistricting in twice as many seats as the Democrats do, and an advantage in control in most of the remaining seats.

In 2012, despite having Obama on the ticket, the Democrats failed to regain the seats they lost in 2010. This failure was due to redistricting, which cemented the Republican advantage in the house. The democrats couldn't regain the speakership until 2019.

The same thing happened to them in 2002, when Hastert survived despite Bush being unpopular. Again, this was due to redistricting.