Of course, because Kentucky has more registered Democrats than Republicans, so there are more democrat voters. This should not be surprising. There are about 1.7 million democrat voters versus 1.1 million republican voters, a fairly significant advantage - about a 55% to 38% advantage for the democrats. The democrats always have more primary votes.
Kentucky, historically, has been a very democrat state (which, again, shouldn't be a surprise.)
So one shouldn't assume how this will translate into the November outcome, based on absolute vote totals in today's primary.