Why is the average number of suspects three or more in Detective Conan?
Three is a number that would make the story go more smoothly. If there were only 2 suspects, the evidence would continuously weigh one one another, making the case go for 5 chapters compared to the usual three. If there are four, or more than such, it would be like watching longer replays of the 50 million suspects case, but these are fillers with no specific information that is important to the timeline, so they should not go longer than 3 chapters.