Is There any reason why CkEditor 5 is adding <p> tags by itself after using any plugin from toolbar?

I have a simple html:

<span>Foo bar</span>

Once I use a bold tag plugin to "bar" keyword from toolbar the html becomes.

<p>
    <span>Foo<strong>bar</strong></span>
</p>

Why CKEditor5 does this ? Why it adds

tag ?

Is there any role of below functionalities which cause this run time conversions? if yes how can I get rid of it? :

1. Schema: https://ckeditor.com/docs/ckeditor5/latest/framework/guides/deep-dive/schema.html
2. Editor Engine:https://ckeditor.com/docs/ckeditor5/latest/framework/guides/architecture/editing-engine.html

Thanks in advance.