In Honda's 4-cylinder engines they have shown they are able to make more power with DOHC heads than SOHC heads.

In Honda's 6-cylinder engines they have shown they are able to make plenty of power with SOHC heads so no need for the added cost of DOHC heads. The only DOHC V6 that Honda makes is in the NSX.

3.2 liter DOHC V6 in the NSX makes 280 hp, the 3.2 liter DOHC V6 in the TL makes 258 hp. The NSX engine has a much higher redline and exotic bits inside of it like titanium connecting rods and stuff.