Why they were able to spam? Can it happen again? It's a very serious attack. What if genuine (non-spam) on-chain transaction demand increases 10x? Would it b

Why they were able to spam? Can it happen again? It's a very serious attack. What if genuine (non-spam) on-chain transaction demand increases 10x? Would it be harder to spam if block size limit increased from 1MB to 32MB or 1GB?