Sola Scriptura is disallowed by Catholics because it doesn't say in Scripture in the words they each individually want to hear, that it is the case.
And yet there are scores of Catholic doctrines, disciplines, teachings, whatever you want to call them, that are not named by name in Scripture that the Catholic church teaches as true.
For example, show me in Scripture where the following Catholic teachings are found by name.
catholic
pope
eucharist
sacraments
annulment
assumption
immaculate conception
mass
purgatory
magisterium
infallible
confirmation
crucifix
rosary
mortal sin
venial sin
perpetual virginity
apostolic succession
indulgences
hyperdulia
catechism
real presence
transubstantiation
liturgy
And then explain to me why exactly, sola Scriptura is not valid.....
Me! I know!!!
Because if they admit Sola Scripture is valid the entire Roman Catholic system goes down the tubes. They like the system as is because it helps them control people and makes their god managable.
That's easy. Because Scripture doesn't explicitly include by name the above Catholic teachings.