Elon Musk wrote:

"Temporary emergency measure," tweeted(opens in a new tab) Musk in a reply to a user posting about the login requirement. "We were getting data pillaged so much that it was degrading service for normal users!"

Mashable wrote:

At the time, it appeared to be a measure to block AI companies from scraping data in order to train its language models. It also seemed like a maneuver to push visitors into registering an account in order to grow Twitter's monthly active user base. As Mashable previously noted, in 2015, Twitter shared that "500 million people" visited the platform on a monthly basis without logging into an account.

Whether the decision to force visitors to login to a Twitter account is actually temporary remains to be seen. Neither Musk or Miqdad shared any timeline for once again enabling Twitter access for visitors without the login requirement.