Because nolock is not "go faster stripes" ? More seriously, probably because the nolock hint is performing a scan which needs to read more pages due to reading in allocation order.
Check out these links for more reasons not to use nolock:
Allocation order scans with nolock
Consistency issues with nolock
Transient Corruption Errors in SQL Server error log caused by nolock
Dirty reads, read errors, reading rows twice and missing rows with nolock