Ford is betting that solid-state batteries will cut EV costs

Too bad, toyota got there first.

Why is it that cars with IC engines do not have solid state batteries, instead of the old lead batteries?

Cost and reliability. The weight and size difference between an Li battery and lead acid battery is insignificant in something as large and heavy as a car. Lead acid batteries are not prone to the thermal runaways that plague Li batteries. We have occasions where I work where the Li batteries on GPS units and laptops left in cars explode and burn. For the auto maker a lead acid battery is one less thing to go wrong, start a fire and force a big costly recall. Absorbed glass mat batteries are maintenance free and usually last 5-6 years. Why fool around with potentially flammable Li batteries?

Motorcycles however are different. Space and weight matter greatly. So does size when trying to package everything in minimal space. You see Li batteries turning up on some motorcycles for this reason.

Why is it that cars with IC engines do not have solid state batteries, instead of the old lead batteries? They would weigh less, take up less room, and probably last much longer. I keep a small lithium battery in the trunk to use as a jumper battery in case the lead battery goes dead. I have had to use it a few times.

If we have to have a mass market for cars and endlessly crowded roads, then electric is the only hope if we are serious about the climate emergency. But, and it is a big but, the electricity must come from clean green sources otherwise it defeats the point of such cars.