There are instances in the Talmud (usually fleshed out by the Rishonim) where we learn a concept that is **so logical** that we don't need a pasuk or drasha to teach it to us, THAT'S how logical it is.
A few examples:
"המוציא מחברו עליו הראיה"- If my ox gored and killed your pregnant cow and the cow’s fetus was found dead at its side- and it is not known whether the cow gave birth before (ie unrelated to the goring) or whether it gave birth after the ox gored it, if you want me to pay you have to prove the latter because: "the burden of proof rests upon the claimant" Bava Kamma 46a
"כל דאלים גבר"- In a financial dispute between two people where there is neither evidence nor presumptive ownership for either litigant, "whoever is stronger prevails" Bava Basra 34b
"כְּדֵי שֶׁלֹּא יְהֵא חוֹטֵא נִשְׂכָּר" - If dough became impure accidentally, one need take 1/48 for challah. However if the dough became purposely impure, the amount for challah one must take is 1/24. Why? "so that the sinner does not profit [from his sin]" Challah 2:7 (expounded further here)
My question is why is svara used sparingly as a halachik source/ reason only in certain areas? "Don't kill" and "don't steal" are both pretty obvious- yet we have explicit p'sukim telling us not to.
Why isn't svara applied for these two or for any other seemingly logical mitzvos?
Edit: the examples listed above don't explicitly state the word "svara" even though that's the concept at work: Thus here are links for each that explains how each is a "svara"
המוציא מחברו עליו הראיה - see "הכלל ומקורו" number 3
כל דאלים גבר- under “מקור וטעם”
כְּדֵי שֶׁלֹּא יְהֵא חוֹטֵא נִשְׂכָּר- under “מקור”