WHY did they glass in the drain???

[drewmitch44]

im sanding and grinding today and i decide to work on the open hole thats got that wooden cover over it. I cut out sections of the floor since the picture and tested the foam to see if its waterlogged. Its not but anyways, the prev owner had blocked the drainage holes with fiberglass and if water gets in on the bow its got nowheres to go. so i opened those holes right in the center on eather side of the center stringer. i know everything is good on the bow part under floor i just took out a gas tank that prev person has filled with foam. there is a little bit of moisture in the place above where the holes were pluged but i mean little bit. Just makes me not understand why they would do that?? I was waiting for water to come flowing out when i drilled through the resin. Nothing. I fingered the hole a little and i can feel foam in there but it is dry. i made a nice tool for testing the foam. I can drill small holes in the floor and i have a water pipe for a 4hp evinrude like a skinny pipe that i push into the foam and then i get a clothes hanger and push the foam out. That way it takes like a little sample of the foam the whole way down.