Because Christians are not yet perfect and glorified on this Earth so remember some of them bore thirty, some sixty and not yet a hundredfold. When it comes to agriculture how often do you keep the soil in condition? Even when the soil is already well-prepared there might be some thorns and weeds so God intervenes so there will be more fruit. In John 15:1-8 we read that the Father purgeth the branches so it bears more fruit. The more I look at the illustration the mature believer and the immature believer both bear fruit but the degree is different. The immature believer starts bearing a few and that person is a useful branch. God knows who the false branches are and who the true branches are. Unsaved people are cast away while true believers can only expect to be chastised whenever they sin (Hebrews 12:5-7).
When it comes to the Christian life bearing fruit for God is not going to do well with the world in the long run. Sure the Christian pastor can get praise from the public for helping out in disaster reliefs but when he preaches the Word of God, he can expect to be criticized severely. It does not matter if the world should turn against the Christian for standing by God's Word. After all, John 15:18-20 has Jesus saying to the disciples, "If the world hate you, ye know that it hated me before it hated you. If ye were of the world, the world would love his own: but because ye are not of the world, but I have chosen you out of the world, therefore the world hateth you. Remember the word that I said unto you, The servant is not greater than his lord. If they have persecuted me, they will also persecute you; if they have kept my saying, they will keep yours also."