Say, the year it is granted the patent costs $1000. The next year, $2000. Ten years since granting, a bit more than million, etc.

If this patent fuels your hockey-stick growth, you have no trouble keeping it.

Keeping a patent defensively becomes much less affordable.

Sharing patent rights for a part of the profit becomes a reasonable way to keep the patent for a few more years.

Even megacorps will eventually face the cost of keeping a patent, and decide to abolish it before it expires, just for economic reasons.

Administration does not become any harder, or more expensive.

[Edited: spelling]