If you just use the 2021 theme as an example, and you add a container and add a bg to it to see the issue easily , the alignment by default is NOT full width, we have a toggle for wide and for full, so the default should be narrow, not 100% of the editor. you apply the follow style on the back end for the alignment if nothing is added...
body .wp-block[data-type^="toolset"]:not([data-align^="full"]), body div:not([class]) > .block-editor-block-list__layout > .wp-block:not([data-align^="full"]), body .tb-container > .block-editor-inner-blocks > .block-editor-block-list__layout > .wp-block:not([data-align^="full"]) {
max-width: 100% !important;
width: 100% !important;
}
I always override this in my editor-styles with something like the below, but I'm confused why the above is ever needed because you are forcing a "normal" aligned block to become an align-full basically there are alignment in most themes for the .wp-block class I see no reason to override that on an non-aligned block
.wp-block,
.wp-block[data-type^="toolset"]:not([data-align^="full"]),
div:not([class]) > .block-editor-block-list__layout > .wp-block:not([data-align^="full"]),
.tb-container > .block-editor-inner-blocks > .block-editor-block-list__layout > .wp-block:not([data-align^="full"]) {
max-width: $wrapper-width-base !important;
z-index: 10;
}