He has always walked a lot of guys (as most strikeout pitchers do). MLBTR's summary:
Robertson, 38 in April, has a lengthy track record of success as a major league reliever. In nine straight seasons from 2010 to 2018, he threw at least 60 innings while never posting an ERA higher than 3.82. Though his control wasn’t always pinpoint perfect, he never had a strikeout rate lower than 26% in any of those seasons. For reference, this year’s league average for relief pitchers was 23.6%.
Unfortunately, that long stretch of reliability came to an abrupt halt in 2019. After signing a two-year, $23MM deal with the Phillies, he only made seven appearances due to injuries, eventually culminating in Tommy John surgery. That kept him out of action for most of that year and all of 2020. He returned to the mound in 2021, starting with that summer’s Olympics and then joining the Rays for 12 appearances after.
That was enough for the Cubs to take a flier on Robertson for 2022, when he truly got back into form. He tossed 40 1/3 innings for the Cubs with a 2.23 ERA and 30.9% strikeout rate. The walks were on the high side at 11.5%, but they didn’t stop him from being tremendously effective, racking up 14 saves in that time. He was flipped to the Phillies prior to the trade deadline and continued in similar fashion. He threw another 23 1/3 innings for the Phils with a 2.70 ERA and 30.3% strikeout rate. The walks became more of an issue, jumping to a 16.2% rate after the deal, but he still added another six saves and three holds. He was able to add another 7 2/3 innings in the postseason despite straining his calf while celebrating a Bryce Harper home run, posting a 1.17 ERA in that time even though he walked 15.2% of batters faced.
I would not have given him $10 million but then I wouldn't have given Knebel $10 million either (or signed Familia at all).