First of all: I want to say that this question is not at all bad.
In Latin, lego, legere, lēgī, lēctus “to read” belongs to the third conjugation, while rīdeo, ridēre, rīsī, rīsus “to laugh” belongs to the second conjugation. As you can see, they are completely different in each of the four principal parts. So it is not so much a question of similar verbs developing differently as of very different verbs becoming more similar. Languages work in both ways.
Latin had a fair number of verbs with a perfect participle in –ūtus, for example secūtus from sequor “to follow”. In Romance languages this form has spread to a large number of different verbs, including French venu, Italian venuto, where it replaced the ending of Latin ventus, but this has not by any means happened to all verbs. For example, it affected lego, but not rīdeo.