Yes, the reason is that no human being was in heaven until Jesus died, so no one asked them to pray for them in heaven in the Old Testament because they weren't there yet. The righteous dead were in the "bosom of Abraham", waiting for their Savior.
The Old Testament was written before Jesus was born. The New Testament does not list very many prayers, and you have to remember that most of the people mentioned in the New Testament were still alive when the "books" of the New Testament were finished being written, so they would obviously not have been petitioned in heaven to pray for anyone here on Earth if they were still alive here on Earth themselves.
Goodnight.
That provides no excuse, as the PTDS doctrine includes praying to angels, while after the Lord's resurrection heaven abounded with believers, yet there is still not evidence of anyone praying to anyone in heaven but the Lord, and the Lord's own instructions on the manner in which believers are to pray specifies it is to Father God, and the Holy Spirit directly prays to God, and the believers immediate access to Him is made clear, and Christ alone is set forth as the all sufficient, able and available mediator in heaven btwn God and man.
Yet as Scripture is not the supreme authority for Catholics, and actual Scripture warrant is not necessary for her doctrines, thus she teaches traditions of men as doctrines, and then abuses Scripture by trying to support her tradition by it, but which at least makes her deception more manifest.
And where's the evidence that this is a place other than Heaven?
most of the people mentioned in the New Testament were still alive
There was a whole slew of saints, however, who under your theology would have been with Christ in Heaven. Yet none of the leaders of the church mention praying to them in any of the epistles.
Rather, the epistles stress the sufficiency of Christ. They stress that one can enter straight into the presence of God because of what Christ has done. In fact, Jesus said we can now stand and pray "in His name" which is far better than petitioning any saint in Heaven.