Because seeing (oti bleponte). In the parallel passages in Mark 4:12 and Luke 8:10 we find ina with the subjunctive. This does not necessarily mean that in Mark and Luke ina=oti with the causal sense, though a few rare instances of such usage may be found in late Greek. For a discussion of the problem see my chapter on "The Causal Use of Hina" in Studies in Early Christianity (1928) edited by Prof. S.J. Case. Here in Matthew we have first "an adaptation of Isaiah 6:9 f. which is quoted in full in v. Matthew 13:14 f." (McNeile). Thus Matthew presents "a striking paradox, 'though they see, they do not (really) see'" (McNeile). Cf. John 9:41 . The idiom here in Matthew gives no trouble save in comparison with Mark and Luke which will be discussed in due turn. The form suniousin is an omega verb form (suniw) rather than the mi verb (sunihmi) as is common in the Koin.