He is younger, cheaper, signed long term, and I am not sure the Bonino in the three year stretch between this past year and his first Cup in PIT (2016-2017, 2017-2018, 2018-2019) has been any better than Kerfoot has been in his first three years in the league... And I would bet on Kerfoot progressing as a 26 year old who is healthy and was quite effective in the playoffs over a 31 year old Bonino coming off of a career year and is likely to regress back to a level of play which could easily be worse than Kerfoot next year.
If we lose Kerfoot to expansion, or trade him for a pending UFA like Bonino, we are going to need his money to find another Kerfoot next year. It is not like there is a shortage of options in UFA, but I think Dubas would rather have Kerfoot on his roster for a year and then lose him in expansion (which has value in itself, since we would not lose another valuable asset like Holl to expansion instead) than trade for a marginal upgrade at best, who costs more cap, and then is a UFA we'd need to re-sign or replace for likely the same amount of money as Kerfoot, but with a lot less upside.
Dubas is probably done with any major moves. Some even think he won't be giving out any kind of PTO's or make any more minor trades/signings. I think that comes down to whether guys come back from Europe this year, whether there will be an AHL season, and how the taxi system will work. If certain guys who would typically be in the AHL are on the taxi squad instead, then he almost certainly needs to sign a couple of forwards at the very least.