Why do I need to invest budget in brand campaigns?

You need to take advantage of branded terms to own as much of the search engine real estate as you can.

Investing in branded keywords gives you an added boost. Not only will your website show up organically, your branded ad will also show up, too (most likely in the prime real estate: at the top of the SERP and bedside that of the OTAs)

Brand messaging - You can entirely control the way your brand comes across in a search engine results. 

Be Competitive - In order to drive as much branded traffic to your own website, you need to compete with the OTAs who are also running campaigns against your brand name. If you don't have campaigns running for your brand, the OTAs will direct a lot of branded traffic to their own sites.