Why trade Hronek after him and hughes were the best pairing in the league

I don't think Hronek would be worth that much.

he wants a big contract iirc 8 million

Hronek's a great defenseman, but his play fell off in the second half of the season. He had 29 points in 33 games, then had a cold streak in December. The media started asking for interviews and there was more pressure on him, he had 19 points in the final 48 games. Based on his refusal to do interviews all season and his exit interview today, he doesn't like playing in a major hockey market and he doesn't want to deal with the pressures that comes with being on a Canadian team, He's still a 40-point RHD who can play in both zones excellently, but it appears he'd prefer to play somewhere quieter.