Your claim was that any change to the ASIC was the same design cost. But really? A 40-bit routing table design, where there is a 32-bit fall-back to preserve the top 8-bits vs a 128-bit routing table design. Why would these be the same cost?
When would you have done it? When the hardware was 5 years old? 10 years old? I've been on change operations where the hardware was over a decade old and our biggest concern was making sure we had replacement PSUs on hand since the thermal shock of a reboot might take them out.
This is the problem, you have absolutely no idea what anything costs or how it works - you're simply thinking "lifting those bits sounds heavy, what if we made them lighter?" as though a committee of engineers, designers and industry didn't spend a lot of time considering exactly that problem.
If you could add 1 byte in software and be done with it, it would have already happened.
You are arguing that all change has the same cost. I don't see your reasoning for this. A smaller change to a system has a lower cost in R&D, and a lower cost in manufacture.
Although it is probably true that the cost of updating all equipment dominates the cost of redesign, this is only an issue for a big bang update rather than a rolling upgrade.