Well, I-10 doesn't go to San Diego and I-8 is not always snow free since it crosses the Laguna Mountains at an elevation of 4190 feet (1280 m). Just saying...
Yep. It is *because* of that occasional snow and road closures on I-8 (just like I-40's black ice near Flag, and I-70's snowed-in closure both sides of the Eisenhower Tunnel this past May), that I-10 remains the safest transcontinental option year-round. And that includes westbound to San Diego from Tucson or anywhere else.
Tangentially, taking I-8 to/through San Diego in a Tesla hasn't been a consideration for years - due, in large measure, to the I-10 SC-related delays. One simply takes I-10 through LA, has dinner, and hangs a left to get to San Diego - which for context for those unfamiliar with the area, is just an hour or so past Orange County.