How does it give the DNC and RNC more power?
If you can't run for another term, you're not really going to be giving a shit about the DNC or RNC at that point. On the other hand, if you're Pelosi and want to stay in your position for 35 years. Basically leading the entire party for 20+ years. Yeah, you'll listen to the DNC or have basically become the DNC at that point. See when your career for your rest of your life is in the balance, you'll do as you're told. On the other hand, if you know this is just a 6 year period of your life or whatever, you've got the freedom to actually try to make positive change.
I'd also be in favor of whatever keeps the 85 year old Pelosi's and 83 year old Mitch McConnell with mental decline from sitting in those seats.