Grenades, as we know them today, were not widely used during the 15th and 16th century for a number of reasons. One of the main reasons is that the technology for creating and using grenades did not yet exist during this period. The first hand-held grenades were developed in the late 16th century, and these early versions were relatively simple devices that were filled with gunpowder and had a fuse attached.

Additionally, the tactics and strategies of warfare during the 15th and 16th centuries did not yet involve the use of grenades. The primary method of warfare during this period was still armored knights charging on horseback and infantry armed with pikes, swords and bows. The use of firearms had not yet become widespread, and the technology for creating effective firearms was still in its early stages.

Furthermore, the cost and complexity of producing grenadiers and the grenades themselves were not yet viable, only a few armies could afford and maintain them.

It's worth to mention that there were some examples of early versions of grenades being used during this period, but these were relatively rare and not yet widely adopted by military forces.

It wasn't until the 17th century that grenades started to be used more widely in warfare.