The reason is quite simple
Laser vs. Plasma (or Torch) Cutting
Generally speaking, laser-cut steel target plates are stronger and longer-lasting than plates cut by gas torch or plasma. The reason is quite simple “Heat softens steel. With laser-cutting, the heat penetrates just 1/16″ into the surrounding steel. With a torch or plasma cutter, the heat can penetrate up to 1/2″ into the steel from the edge of the cut. Welding 500 Brinell steel softens it for the same reasons.”
Bolts vs. Welds
Bolt-on target plates are normally better than plates with welded attachments for three reasons. First, the heat from the weld penetrates the steel, reducing the surface hardness. Second, the weld is generally more brittle and is usually the first part to fail. Lastly, with a bolted attachment it is much easier to detach and reverse the target plate, extending its useful life. Likewise, bolted fixtures allow you to easily swap plate designs or replace a worn-out target.