Back than there wasnt much 2.4Ghz traffic so the higher bandwidth helped. In a densed wifi environment 20 mhz helps more than 40mhz. It is possible to apply 40mhz on channels 1 or 13 which will give less of a chance of interference. back than wifi practical rates were a lot lower than now.
Blog Cisco When and How to Use 20mhz vs 40mhz vs 80mhz When and How to Use 20mhz vs 40mhz vs 80mhz The word network is a simple word of seven letters, but is it that simple? Let's take a broader look to understand it rightly. If putting it simply, whenever we think of or talk about some inter-connected stuff or location, we refer it as a network. With 20MHz-wide channels on 802.11n, you can only get the 72.2, 144.4, or 216.6Mbps top PHY rates (for 1-, 2-, and 3 spatial streams, respectively). Going to 40MHz-wide channels makes it 150, 300, and 450 Mbps, respectively. What users do not know is that to obtain this speed it is necessary to act on the router and configure the Band Width item (in some routers also called Band Width, WiFi Bands or WiFi 20 MHz or 40 MHz).