The magicians would seem to have been able to increase the plague, but not to remove it; hence, Pharaoh's application to Moses, the first symptoms of yielding.

The magicians did so - A little juggling or dexterity of hand might have been quite sufficient for the imitation of this miracle, because frogs in abundance had already been produced; and some of these kept in readiness might have been brought forward by the magicians, as proofs of their pretended power and equality in influence to Moses and Aaron.

And the magicians did so with their enchantments, &c. By their secret wiles and juggling tricks:
and brought up frogs upon the land of Egypt, that is, some few, as a proof of their art and skill, and to show that Moses and Aaron did but what they could do; but what they did either were only in appearance, deceiving the sight of Pharaoh and his people, or real frogs were brought to them by the help of devils, but not in such numbers: and besides, this was adding to the plague, and not diminishing it; had they done anything to the purpose, they should have removed it at once, or destroyed the frogs; but that they could not do, of which Pharaoh being sensible, he therefore entreated for the removal of them by Moses and Aaron. To this plague there seems to be some reference at the pouring out of the sixth vial, Revelation 16:13.

the magicians did so with their enchantments--required no great art to make the offensive reptiles appear on any small spot of ground. What they undertook to do already existed in abundance all around. They would better have shown their power by removing the frogs.

This miracle was also imitated by the Egyptian augurs with their secret arts, and frogs were brought upon the land by them. But if they were able to bring the plague, they could not take it away. The latter is not expressly stated, it is true; but it is evident from the fact that Pharaoh was obliged to send for Moses and Aaron to intercede with Jehovah to take them away. The king would never have applied to Moses and Aaron for help if his charmers could have charmed the plague away. Moreover the fact that Pharaoh entreated them to intercede with Jehovah to take away the frogs, and promised to let the people go, that they might sacrifice to Jehovah (Exodus 8:8), was a sign that he regarded the God of Israel as the author of the plague. To strengthen the impression made upon the king by this plague with reference to the might of Jehovah, Moses said to him (Exodus 8:9), "Glorify thyself over me, when I shall entreat for thee," i.e., take the glory upon thyself of determining the time when I shall remove the plague through my intercession. The expression is elliptical, and לעמר (saying) is to be supplied, as in Judges 7:2. To give Jehovah the glory, Moses placed himself below Pharaoh, and left him to fix the time for the frogs to be removed through his intercession.