What makes you think that is what they did? As you know, or should know by now , the stories are a myth. It makes more sense that each one made up their own genealogies. There is nothing in the Bible that hints or even implies that one is Joseph's and one is Mary's. In fact for a while in the past it was argued the other way around. The odds are that Jesus, like most Jews, did not know his genealogy. That appears to have been limited to the priestly order.
No, it is the claim that they were descended from them by later apologists. The two lists both appear to be of Joseph's line. Also back then illiteracy was the norm, not the exception. And since Christianity appealed mostly to the lower classes at that time the odds are very high that very few of them could have checked the records and they would probably not even have thought of ti.
Why? What makes one more trustworthy than the other?
Oops, someone has been listening to apologists again. I am not sure of the dating of Acts but the Gospel of Luke, not "Luke's Gospel" is dated no earlier than 80 CE.
No, Mary would have been ancient by the year 80CE. Actually she would have been dust by then. You should not get your "evidence" from suspect sources. One thing that you need to remember: Believers, such as apologists only want to believe. Scholars, whether Christian or secular want to know. The latter publish in peer reviewed journals where others can and will point out any errors that they made. Apologists use their own press and unless an error is extremely bad they pretty much keep their mouths shut.
Here is a long excerpt from an article on when they were written and why scholars have this belief, spoiler alert it is later than 90CE:
Most modern scholars who write about Acts favor an intermediate date, i.e., c. 80-c. 90 CE, and they cite a number of factors to support this dating. The destruction of Jerusalem and its Temple by Roman armies in 70 CE is not mentioned in Acts but is probably alluded to in Luke 21:20-24. But Acts could not have been written before c. 90 CE, since the author seems to be ignorant about Paul's letters, which were not collected and circulated before that date.
[1]
Several implications follow from dating Acts in this intermediate period. It becomes unlikely that Acts provides us with an eye-witness account of the life of Paul. The author is a generation removed from the time of those persons he writes about and, although he devotes sig-nificant attention to Paul, he fails to mention important things about him. For example, Paul's letters reveal that he claimed to be an apostle and that this status was vital to him. But in Acts 1:21-22 the criteria for being an apostle definitively exclude Paul from membership in this group. Further, Acts 1:13 has a list of eleven apostles, to which number Matthias is added to replace Ju-das (Acts 1:26). Acts makes it clear that the number of apostles cannot be more or less than twelve and that Paul is not included among them. It would be highly unlikely for an author who was also a companion of Paul to go to such lengths to exclude Paul from an office that he so vig-orously claimed for himself.
[2]
A growing number of scholars prefer a late date for the composition of Acts, i.e., c. 110-120 CE.
[3] Three factors support such a date. First, Acts seems to be unknown before the last half of the second century. Second, compelling arguments can be made that the author of Acts was acquainted with some materials written by Josephus, who completed his Antiquities of the Jews in 93-94 CE. If the author of Acts knew of some pieces from this document, he could not have written his book before that date. Third, recent studies have revised the judgment that the author of Acts was unaware of the Pauline letters. Convincing arguments have been made especially in the case of Galatians by scholars who are convinced that the author of Acts not only knew this Pauline letter but regarded it as a problem and wrote to subvert it.
[4] They especially call attention to the verbal and ideational similarities between Acts 15 and Galatians 2 and show how the dif-ferences may be intended to create a distance between Paul and some of his later interpreters and critics.
You can read the whole article here:
When and Why Was the Acts of the Apostles Written? | Bible Interp