Even something like gold with no value production - whose price is quite stable because of that by the way - has value because people want it for jewellery and industry.
“Most” is the key difference: a share of Tesla is fractional ownership in a real business which has proven capable of selling real products which people want. Some fraction of that is definitely speculative but far from all of it, and there's no reason to think that the value would decline to zero under any feasible economic situation.
A Bitcoin, in contrast, has no value other than what you can convince someone else to buy it for. Nobody needs it to conduct business, it's trivial to set up competing blockchains, and the deflationary model is designed to make you profitfrom everyone who starts buying later despite not having created any new value.