Why should trademarks expire? If I'm doing business as Bob's Company, and I spend 15 years building up my good name and it's known for doing quality work, why should someone be able to come in and claim that they're also Bob's Company, just because some time has passed?
Why should companies live forever? If they have 'personhood' then they need to die at some point... otherwise we have cancerous monstrosities we see currently. That is what happens when any component of something larger (society) lives too long, hogging resources while killing the host.
20 years for trademark is negotiable. That there needs to be an expiration date is not.