This week's book giveaways are in the Cloud and AI/ML forums. We're giving away four copies each of Cloud Native Patterns and Natural Language Processing and have the authors on-line! See this thread and this one for details.
The quick answer is that blockchain technology is very young: although it appeared in 2009 with the launch of bitcoin, the first blockchain platform that allows to build any Decentralized application beyond crypto-currencies is Ethereum, which is less than 5 years old. When it was reaching a critical mass of developers, around the end of 2017, the crypto-crash happened and this scared off investors, who decided to take a break from this technology. Also, other competing decentralized ledger technologies (DLT) such as Hyperledger and Corda have appeared, so there has been a fragmentation of efforts. On the other hand, the new crypto rally which has started a couple of months ago seems to have injected new enthusiasm into the technology and new projects have started to appear. Therefore, I believe this is the best time to learn the technology before it becomes mainstream.