It's not straightforward. If you do it wrong you kill people. Your house burns down, you burn your neighborhood down, you electrocute utility workers doing maintenance, you contribute to grid instability which is already a tight balancing act.

Can you make plug and play possible? Sure but you're just shifting the verification to a different layer and then you have to make it illegal to posses or sell any thing but the safe engineered products and you have to spend a bunch on enforcement to make sure only the safe stuff gets put in practice (not to mention replacing all the existing hardware and making it illegal to maintain)...

Modern consumer products and safety rules insulate people so much from the dangerous parts of existence that people get bothered when everything isn't like that and then want to go pet the big stripey orange and black kitty... not realizing that guardrails and safety nets aren't everywhere in existence.

And putting up those guardrails is EXPENSIVE. You want those instead of professional installation costs? Sure but the solar system you bought just got 10x as expensive as a result saving you nothing.

A house costs what... $250-500k to build these days? $10k for a major update to the build is nothing. Requiring expertise to verify dangerous things are done correctly is appropriate.