As long as their "showrooms" don't close, they don't need to care. But, as soon as that starts happening, the will lose those customers who just don't do online shopping (there are many, and will be many for many many years) and those sales where their qualities that you only feel, but not see on a website, win the customer. And those sales that are made on the spur of the moment, because you're walking in the mall and just see that think which catches your attention.
So, it can be a matter where maximizing your revenues now can hurt you in the long run. But, most importantly, as brick and mortar outlets fight for their future survival, somebody could choose to let go of his online sales to win a decisive hand in the traditional channel.
I think your reasoning suggests that brick-and-mortar stores will never be fully obsolete.
As a manufacturer, I don't see how shutting down my online presence would benefit me. Simplified, there are three types of customers. The first shop in traditional stores, find what they like, and purchase it. The second browse and purchase online, without ever seeing the physical merchandise. The third browse traditional "showrooms," then proceed to buy from a cheaper online retailer.
With an online and traditional presence, manufacturers capture all three types of customers. If you limit yourself to traditional stores, you force the third type of customer to purchase in-store, because there is no cheaper online alternative. But those customers would buy online anyway, so you gain nothing. And you've completely lost the second type of customer, who only shops online. A simplified model, perhaps, but the principle stands.
I'm honestly not too worried. I like going to the mall. My mother practically lives at Target and Wal-Mart. Many of us like the physical act of shopping, enough to sustain physical retail outlets. Profits may shrink, but that's the free market. You've got to keep innovating to stay in business.
I think you're not considering that it's not only the brands that can make choices; it is the brick-and-mortar shops too. They can choose not to sell some brands, or to give them bad placement. Especially big retailers have a lot of leverage with brands.
So, it can be a matter where maximizing your revenues now can hurt you in the long run. But, most importantly, as brick and mortar outlets fight for their future survival, somebody could choose to let go of his online sales to win a decisive hand in the traditional channel.