What were the conditions that led to the first bail reform movement in the 1960s?

As an outgrowth of the Civil Rights movement and reforms of the 1960s, politicians, think tanks, and legal activists had begun to examine standard bail practices in the courts. They found that the system overwhelmingly disadvantaged the poor and minorities by imposing sizable bails regardless of the financial considerations of the defendants. In 1951 the Supreme Court ruling of Stack v. Boyle had ruled that bail must be individualized, but after a decade, the courts had found no consistent or fair way to implement this.
Throughout the early 1960s, a number of studies found that the risk of a defendant fleeing before a trial was not directly related to the severity of the crime. The previous practice had been to impose higher bails for more serious crimes, regardless of other conditions affecting the likelihood of a defendant's risk of pretrial misconduct. Studies, such as the Vera Institute's Personal Recognizance experiment, found that, counterintuitively, defendants accused of a less severe crime were more likely to fail to appear in court. The Vera Institute used its findings to encourage judges to take factors other than the nature of the crime into consideration when determining bail. It urged judges to consider the defendant's community and family ties and other connections that would likely increase or decrease their risk of misconduct before a trial.
Further studies encouraged the implementation of a ten percent payment of bails in the form of a deposit. It had been found that when a small refundable portion of the bail was set, a defendant was more likely to show up in court in order to reclaim this money than if a larger, nonrefundable amount was paid, as had been the practice previously. This practice was first implemented in Illinois in 1965 and found to be largely successful. It is now a standard practice nationwide.
As a result of the growing concern of unfair bail practices and studies outlining better methods, a National Pretrial Symposium was held in 1966, attended by many leading politicians. This all led to the first Bail Reform Act later that year.
https://law.jrank.org/pages/560/Bail-Bail-reform-strategies.html

https://www.splcenter.org/20170606/two-tiered-justice-system-money-bail-historical-perspective