That makes sense, 2013 was when ASICs were getting popular and started dominating mining. The industry has slowed down significantly since. Presumably they've implemented most of the low hanging fruit optimizations. Antminers from 3+ years ago are still profitable in a lot of areas with <=$0.1/kWh electricity.
This makes sense. In the earlier days of bitcoin we’ve seen substantial improvements in mining every 3-6 months.
We’re talking about significant 100x-1,000x improvements in efficiency and profitability.
To stay competitive, these improvements in efficiency made it necessary for miners to upgrade mining equipment every 3-6 months.
Because of its closeness to silicon fabrication and cheap energy, China emerged as the de facto place to set up these mining farms.
Those previous 100x-1,000x improvements are no longer possible.
The development of mining hardware caught up with Moore’s law.
This is the observation that transistors in a dense integrated circuit doubles about every two years.
It would be fair to assume ~2x improvements in mining every ~2 years.
This would mean that mining equipment would now have a longer shelf life, and no longer be obsolete in a few months.