Second, ACME v2 was designed with additional input from other CAs besides Let’s Encrypt, so it should be easier for other CAs to use. We want a standardized ACME to work for many CAs, and ACME v1, while usable by other CAs, was designed with Let’s Encrypt in particular in mind. ACME v2 should meet more needs.
From the URL:
Second, ACME v2 was designed with additional input from other CAs besides Let’s Encrypt, so it should be easier for other CAs to use. We want a standardized ACME to work for many CAs, and ACME v1, while usable by other CAs, was designed with Let’s Encrypt in particular in mind. ACME v2 should meet more needs.