Why he's a trendy Fantasy Baseball Pick Right Now:
He's pitched well over the last month, (two earned runs or less allowed in his last five starts) and has a nice 3.09 ERA. It also doesn't hurt that his next start is tomorrow against a pretty weak Cubs team.
What to Expect Going Forward:
Some regression but not a complete drop off in performance. He has been slightly lucky on opposing BABIP (.281 versus .313 career) and he's getting lucky on the fly balls turning into homers (7% this year versus 9.9%) career. Still, even with regression factored in, he still looks to be a decent mid to back rotation pitcher on a contending team (or as it turns out the best pitcher on a Pirates team with what has been a struggling starting rotation thus far). His FIP/xFIP indicate that his ERA are likely to be near the 3.75-4 range going forward. I think he'll continue this good stretch against the Cubs but he's going to have some struggles sooner rather than later.
There doesn't seem to be any major changes to how opposing hitters are hitting him as his line drive, ground ball and fly ball rates are all within career ranges. The only real change to his approach is that he's throwing slightly more curveballs than he has in his career (which could possibly help in keeping the regression to a minimum) even then it's not a career high. One interesting thing to note is that he is on track to lead the NL in hit batsmen for the second consecutive year. Point being, he doesn't appear to be any better or worse than he has been the last few years.
While Morton has pitched relatively well (and will likely continue to at least be productive if not a star), the Pirates have under-achieved based on the high expectations set on them after making the playoffs last year. In looking at the team stats on baseball-reference it is easy to see why as he is the only starting pitcher on the Pirates with an ERA+ above 100 (115).
If the Pirates want to make some noise in either the NL Central or Wild Card race they will need Morton's nice stretch to continue for an extended amount of time and hope that Cole (one of my least favorite players after his Carlos Gomez incident) and Liriano are productive once they are activated from the disabled list and maybe go back in time and call up Gregory Polanco in April (or not since I enjoyed the Brewers dominating the Pirates for much of the early season).
One interesting thing to note is that out of players drafted in the third round in the 2002 draft, Morton has the lowest career WAR primarily due to a couple of terrible seasons in 2008 & 2010. While his career WAR is sub-replacement level, he can reverse this with another year or two of solid if not unspectacular pitching.
One thing that is probably out of reach is being the best player drafted in the third round of the 2002 draft (an honor that Curtis Granderson holds and has no threat to have relinquished).
All numbers, data, etc referenced found on fangraphs.com and/or baseball-reference.com