why does bootstrap container not touch sides code example

Example 1: breakpoint bootstrap

// Extra small devices (portrait phones, less than 576px)
// No media query for `xs` since this is the default in Bootstrap

// Small devices (landscape phones, 576px and up)
@media (min-width: 576px) { ... }

// Medium devices (tablets, 768px and up)
@media (min-width: 768px) { ... }

// Large devices (desktops, 992px and up)
@media (min-width: 992px) { ... }

// Extra large devices (large desktops, 1200px and up)
@media (min-width: 1200px) { ... }

Example 2: bootstrap container width

--------------------------------------------------------------------------------------
Bootstrap Container Width			 					| Size        | Class Prefix
--------------------------------------------------------------------------------------
Extra small devices Phones (less than 768px)  			| None (auto) | .col-xs-
Small devices Tablets (greater than equals 768px) 		| 750px       | .col-sm-
Medium devices Desktops (greater than equals 992px)     | 970px       | .col-md-
Large devices Desktops (greater than equals 1200px)     | 1170px      | .col-lg-