The answer to 'why is my stone walkway thin grass' is that the stones or pavers on your walkway are blocking sunlight and preventing grass from growing properly. This is a common issue with stone walkways, as the dense materials and lack of soil exposure can create an environment that is inhospitable for grass to thrive.
Some common causes include the stones being too tightly packed together, the walkway being installed on a solid base like concrete rather than soil, or the stones being too large and leaving little room for grass to grow in the cracks. Over time, the grass may become sparse or die off completely, leaving you with a thin, patchy lawn along the edges of your walkway.