Why did Christians choose the basilica style of building for their houses of worship?

Answer 1

Becase they could accumulate a great amount of people inside. As well they choose it over temples as basilicas were non religios buildings. More over it was usually situated in the middle of the city( forums )

Answer 2

The first Christian churches were modelled of the basilicas of the Romans because they were public buildings, and therefore they could accommodate large crowds. The Christians used the plan of the basilica palatina (palace basilica). This was designed by the men of the governing elite when they stopped appearing at the forum and started to address audiences in these basilicas which were part of their palaces. The Christians used this plan to accommodate the altar and have a place where the priest delivered the sermons.

This is the origin of the rectangular shape of churches and of the apse, the semi-circular or polygonal recess with a semi-dome as roof at the far end of the entrance. The apse was modelled on the exedra of the Roman basilica palatina. The exedra had the tribuna (a seat on a raised floor where the important men addressed the audience or the magistrate heard cases). The Christians replaced the tribuna with the the altar.

The first Christian churches were called basilicas. In Italian some churches are still called basilicas, including very first churches, such as St Peter's, St John's Lateran, St Mary Major, and St Paul's Outside the Walls

Emperor Constantine ordered some churches to be built with a transept, a section that lied across the main building and protrudes on both sides, giving ta cruciform (cross- shaped) building.