How quickly a new tech expands is largely affected by how tightly the winners of the status quo hold onto today. They scratch and claw and resist the new tech until they set it up so that they can be along for the ride.
This is what I call narrative-based thinking.
Someone asks: "Why do we need an upstart like Tesla to come in and prove EVs are viable when we have a bunch of entrenched automakers who could already do it? They must be resisting the technology!"
No, they're not. GM was an early adopter of EVs with the original EV-1. In fact, if I remember correctly they were one of the first ones to show the "skateboard" concept of a BEV, where the floor of the car was batteries and you had 4 electric motors, each at one wheel, which allows for a lot more freedom in the design of the cabin relative to having to wedge an engine up front. Toyota was producing hybrids long before Tesla existed. GM went down the plug-in hybrid path with the Volt and Toyota has gone that direction as well. Nissan had the Leaf before Tesla existed, and Chevy has had the Bolt for a couple of years now. Toyota has been the trailblazer on fuel cell tech with their Mirai. It's not like they've all been sitting on their hands.
Conventional automakers have nothing to fear from EVs, honestly. It's not like the oil & gas industries where other energy sources completely supplant them. It's them changing the technology that propels their vehicles from an internal combustion engine to a battery-fed electric motor. In fact, much of the technology is simpler for them than ICEV.
The truth is that I'm going to guess that every major automaker has been in their boardrooms asking the question "How much R&D should we be spending on EVs so that we'll be ready for the switch when it happens?" Judging by all the recent announcements of automakers jumping in, they've been planning for a long time for this.
Tesla got first-mover advantage in this race, but it's still unclear whether they'll be able to scale and compete with the big boys once the big boys really start rolling. Tesla has not been profitable until recently, and today their profitability is STILL not based on car sales--it's the sale of regulatory credits that has moved them from losing money to actually showing an entire year of profitability. Once other automakers are producing their own EVs, they won't need to buy regulatory credits from Tesla. Can Tesla keep its advantage then? Unclear...
The big automakers haven't jumped into the BEV race because they didn't believe they could make money at it yet, not because they were "keeping alternative technologies down". Now that it's reaching a level of maturity, they're all starting to jump right in.