Why isn't slt laser therapy used more as a first line treatment of glaucoma instead of drops?

Patient preference: In my experience, patient's tend to prefer using medications to lower their iop rather than slt as initial therapy. This gives them more involvement in their glaucoma care, and this adherence to treatment is key to success. Slt is certainly a viable first (primary) treatment option patients can choose, and works effectively in about 80% of patients.

Depends on patient: And physician. Slt can wear off, many patients are afraid of laser. Drops can always be stopped but laser can't be taken back.