'Taken' was the hit that seemed to get the snowball rolling on this stage of Liam Neeson's career. That one dates to 2008.
His wife's death probably didn't help, but this is also just a common career path for older action heroes. I dunno why they don't get tired of it but I guess it's steady work that pays well. Most good roles (any genre) go to younger actors, especially starring roles. If Liam Neeson wasn't starring in 'Death Wish' flicks, then would he be starring in anything else? He would probably have to step down the ladder on prestige & budgets.
FWIW, I think Liam is doing this career stage better than most. Denzel Washington is on the same path and doing okay. Bruce Willis is totally embarrassing himself these days. (Steven Seagal would be the worst embarrassment but he never had a respectable stage to start with.)
I wonder if Tom Cruise will go this way. The Scientology witch doctors cannot keep him looking 45yo forever. He's almost 60 now. He already auditioned for the Liam Neeson job with those 'Jack Reacher' movies.