you must read the bible as one cohesive whole:
Those on the rocky ground are the ones who receive the word with joy when they hear it, but they have no root. They believe for a while, but in the time of testing they fall away. 14 The seed that fell among thorns stands for those who hear, but as they go on their way they are choked by life’s worries, riches and pleasures, and they do not mature. Luke8:13&14
Note in the second example of the parable of the sower, it refers to the seed that fell on shallow ground. People receive the word with joy and go on their way, they believe for a while, but when the time of testing comes they fall away. They must have been in a saved state to get to where they fell away.
The people in the third example, kept getting distracted from the path by the worries and pleasures of this world, but Jesus does not say they walked away, only that they did not mature. We have to accept all of Jesus words concerning this, not just the ones we want to cling to