condition no 1: You have no much backlink
Google usually crawls to the blog late which have less backlinks so you need to make strong backlinks to your blog by commenting in someone other post or something like that
condition no 2: Google Penalize
This condition happens when google penalizes you and even if your blog used to have Google indexing or quickly recognized , after you are penalized, you may have slow updates of blog in Google.
This may happen if:
You make too much of backlinks to your blog and it looks unnatural to Google
Too much of two way Link Exchange may create problem.
Or other violations of Google term.
This condition usually goes after some time automatically but this problem exists for long time in some case.