I have a CDA-9886, and I have come to find out that the sub-out is actually a full range output.
Why would Alpine do this?
The built in high-pass works just fine on the deck, which is good to know.

I find it odd that Alpine has done this.
Does anyone else find this odd?

Their logic is for the consumer to purchase one of their amplifiers with the x-over built in. Up sell, add on what ever you would like to call it. Some head units used to come with selectable low pass filters, found that the % of Alpine amp add on sales had dropped. Also wanted to lower the over all cost of the unit to the dealers, but keep margin up by this amplifier add on sale. This thought may start to change again in the future.

Maybe they were thinking that some customers have boom boxes that are full range in the hatch and like to have outdoor parties. It's easy to switch the low pass on to make it a sub only set up for daily driving, and switch the cross over to full range for parties.