Agreed. Now that the "get rich quick" phase of mining is over, there aren't many incentives for all the costs incurred.

Isn't that the reasoning behind transaction fees?

Transaction fees are for miners, but every full node in the network has to store the whole blockchain forever. There are thin clients using SPV, but we need full nodes for the network to function properly and currently there is zero incentive for it.

Aside from helping the network, there is no incentive to run a full Bitcoin node. But it doesn't take much in the way of resources: a few tens of gigabytes of disk space and a few tens of kilobits/sec of bandwidth. (Don't forget to open a port on your router!) I do it for the same reason I give over an extra SSID to openwireless.org, or run a TOR exit node, or seed any file I got from BitTorrent for a while afterwards: it helps the network.