Two main reasons:
1. Sevilla nearly knocked out FC Porto. The sides were drawn in the Europa League round of 32, and Porto advanced on away goals. Porto won 1-2 in Spain and lost 0-1 in Portugal. By comparison, the Portuguese side won both legs of the Europa League playoff, went 5-1-0 in the group stage, and swept all 4 legs in the knockout stage against Moscow rivals CSKA and Spartak.
2. Sevilla has what Villarreal wants. Villarreal has enjoyed a decade of success among the European elite. But the club is missing a major title to hang its hat on. Enter Sevilla's back-to-back UEFA Cup titles in 2005-06 and 2006-07, not to mention last season's Copa del Rey triumph. Our inaugural title is only 3 matches away.
A bonus reason: Sevilla, like Valencia, thinks that we are the nouveau riche upstarts of La Liga. Let's show them that the traditional order is a thing of the past.