As a CPU engineer, I can say that spectre highlighted channels of information escape that weren't previously considered as vulnerable. That's why it kicked off

As a CPU engineer, I can say that spectre highlighted channels of information escape that weren't previously considered as vulnerable. That's why it kicked off a new batch of exploits. There was a new idea at the heart of it and others built on that idea. It's also important to say that these are not bugs. The design is behaving as intentioned. That the performance differs based off the previous code that the CPU has executed was understood and deameed acceptable because the cost of the alternative was considered too high (either in power, performance or area) than the alternative. That's what it means to be an engineer. You weigh up alternatives and make a choice. In this case, CPUs became fast enough that the fractional part of a bit per iteration became high enough bandwidth to be exploitable, but it needed someone to demonstrate it for it to be understood in the industry. That changed the engineering decision.