Lent began in the apostolic era and was universal in the ancient church. For this reason, Lent is observed by the various Presbyterian, Methodist, Lutheran, and Anglican churches, by Roman Catholics, and by Eastern Orthodox Churches. But it is easier to explain who stopped observe it and why.
In the 16th century, many of the Anabaptists discarded all Christian holy days, on the theory that they were Roman innovations. That was their best information at the time, but today we know that they were wrong. In the late nineteenth century, ancient Christian documents came to light. The Didache from the first century, the Apostolic Constitutions from the third century, and the diaries of Egeria of the fourth century; all which give evidence of the Christian calendar and holy days. The Didache and the Apostolic Constitutions were written in the east, which denies it ever recognized the institution of the papacy. Egeria was a Spanish nun, but her writings also describe practices in the east. All of these documents came to light 300 years after it was too late for the groups who had already discarded Christian holy days.
In many cases, however, Rome was the last place to observe the Holy days. For example, the idea of moving All Saints Day to November 1 did not reach Rome until 700 years after it originated in England, and the idea of celebrating Holy Week as Palm Sunday, Maundy Thursday, and Good Friday, was quite elaborate in Jerusalem before the early fourth century but did not spread to Rome until the 11th century.
Advent began in medieval Gaul and spread to Rome from there. Lent, on the other hand, appears to have originated in the apostolic age. The Apostolic Constitutions attribute the observance of Lent to an apostolic commandment. We can’t verify that, but we also can’t disprove it. The Anabaptists gave rise to or influenced the Amish, the Mennonites, the Baptists, and the Plymouth Brethren. The Puritans, who were Calvinists, had similar views on worship, which is why they made Christmas illegal in Massachusetts at one time. (Some Mennonites, however, never rejected the Christian holy days.)
In the 19th century, the established denominations were slow to spread west of the Appalachians, which was the frontier at the time. The area was thinly populated and there were very few seminary-trained clergy. The lay people had been converted at camp meetings without any church background. They were influenced by the groups that had rejected Christian holy days, but frontier conditions were not conducive to structured liturgical worship anyway. They weren’t aware of the Christian holy days, and they didn’t have the equipment, the facilities, the education, the authorization, or the training to conduct liturgical worship. Therefore most of the religious groups that were formed in the United States in the 19th century do not have a custom of observing Lent. This environment had some influence on individual congregations in denominations that have historically observed the Christian holy days-so you will occasionally find a Methodist church that does not observe Lent.
Gradually, the holy days have returned to the churches that had discarded them. The restoration quickly began with Easter. Christmas followed in the 19th century, and Advent and Holy Week became widespread among them in the 20th century. Lent is mounting a come-back in the 21st century.
And that is why Lent is back.