Yes it is a matter of tradition, but it also has to do with the comfort of the catechumens. It is understandably uncomfortable for them to have to sit there while people trip over them to get to the Communion line.
Usually, when the elect are dismissed, they don’t just go home. They go to another room in the church and study the Scriptures for that Sunday with the RCIA director. They may also have an inquiry. This allows for them to gain a deeper understanding of the word and how it applies to them, not having been baptized, before they come to know the Word–Jesus Christ as He is really present in the Eucharist.
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