This is just my opinion, and keep in mind that I converted to Catholicism from Evangelical Protestantism, so I have no background of Catholic small-t traditions.
I think that perhaps the saints were so strict about keeping the small-t traditions because these traditions contributed to unity in the Church. Even though we like to think that Catholicism was The Only Christianity in the past, this really isn’t true. There were always heretical teachings being bandied about, and “messiahs” claiming to be another Christ. Also, there were various sinful lifestyles that could tempt people away from the Church and Jesus Christ (e.g., earning a living as a bandit or a prostitute instead of doing something good and honorable that made less income).
A careful adherence to a “lifestyle” of certain practices and disciplines is very helpful to holding people together in a strong “team.” Consider sports teams–they all have their “uniforms” and “colors”, cheers, mascots, rituals, etc. These “traditions” help the team members and also their fans to remain a tight unit, committed to the team and to each other.
Those people who started to deviate from the small-t traditions were possibly more likely to drift away from the Church and Jesus, and of course be in danger of hellfire as they fell into a state of mortal sin.
So of course the saints would emphasize, with very strong language, the importance of staying with the group and doing what everyone else does, and not trying to be a “loner”. The concept of “doing your own thing” didn’t exist back then in society or in the Church.
Today, Christian unity is still a major issue in the Christian Church. Not only do we have a “split” Christian Church (Catholic, Orthodox, Protestant), but we have a great deal of diversity within those three groups. I honestly don’t think the saints of the past anticipated any of that diversity. Their world was very small, consisting only of the land and people where they lived. E.g., they couldn’t conceive of a society in which women played an equal role in the workplace and the government. They couldn’t conceive of a society in which so many children lived past infancy. They couldn’t conceive of an internet which shrinks the world.
My personal opinion is that the saints’ statements about small-t traditions were appropriate and necessary for their times and people, but that these statements make no sense today in a diverse world in which most of us are capable of understanding how people can have different religious practices, but still be One in Christ.
The saints were humans, not divine. Their writings are not Sacred Scripture–and even in the Sacred Scripture, there are practices that were once mandatory that no longer apply to us who under the New Covenant. And most important, we cannot pick and choose which of the saints’ admonitions to follow and ignore the rest of their writings–if we are going to elevate the teachings about adherence to small-t traditions to the level of dogma, then we must elevate ALL of their teachings to dogma.
Finally, we are to be guided in our practices by Holy Mother Church, and our Church does not ask us to adhere to small-t traditions. Whether we agree with our Church is not important. The Church is guided by the Holy Spirit, and we can trust our Church. In this day and age, it is by our obedience to Holy Mother Church, not by consistently practicing a list of small-t traditions, that we maintain our unity with Christ and stay safe from drifting away into heresy and/or sin. Trust and obey–that’s more important to Christian unity in today’s world than saying certain prayers, making certain gestures, or wearing certain articles.