Because even if the rate is not drastically better today, the renewals surely will be better (for Plan G) tomorrow.
Mutual of Omaha on February 12, 2014 had a post purporting the benefits of Plan G.
This was covered in depth for our members in this webinar, where not only are the benefits shown, but the salesmanship to go along with it are explored. The only company in the market paying commissions on the Part B deductible is New Era (and sister company Philadelphia American). This means, with the other companies, you are not getting paid commission on the deductible, anyway.
In my opinion, it is far better to separate yourself from the competition by saving your client the most money today, and at renewal time, by strongly recommending Plan G.
Remember, though, that many seniors just won't get it. Some are not capable of understanding the numbers and just want the convenience of Plan F. Don't be discouraged when you encounter this. They just don't want to be bothered. In the end, the customer is always right, and I'm happy to sell them what they are looking for.