Why choose tsuke-nobi after a double keima against hoshi?
Black at the 3-3 point is a special strategy that requires supporting stones in the area.

In the fuseki, without supporting stones, black's objective is to separate white, with 3 main options:


tsuke nobi against the pincer stone (your diagram)
tsuke nobi against the pincered stone
5-5 point


38 Basic Joseki is an older book that favors the first option. In more modern play you'll see the two other options as well. The tsuke nobi keeps the white stones separated, while the 5-5 point will put more emphasis on cental influence.

This page shows a very recent variation from AlphaGo.