Because our technology doesn't magically appear out of nowhere. Even the simple DIY "lifehack" you can assemble from $5 worth of RadioShack parts has huge supply chains hidden behind it, staffed by hundreds of thousands of people. On top of that, all those supply chains are full of circular dependencies. A chip needs a fab. A fab needs computers. Computers need chips... and screws. Screws need metal and precision manufacturing machines. Precision manufacturing machines need computers and screws. Metal mining needs computer and screws. Etc.
If the climate situation gets to the point of crashing global supply chains, say goodbye to all modern technology. Whatever's left will degrade quickly, and we'll be back to preindustrial levels, but with no easily accessible dense energy sources to bootstrap another industrial revolution.
This is why I keep saying that the most important goal right now is not to protect the planet, not to protect the human species, but to protect our technological civilization. If it collapses, we'll still be there (albeit in reduced numbers). But our civilization won't recover for millennia.