this is not true. Even during the best times of ZTTL we always had very few full nodes.
Nobody wants to do this job, everyone expects that there will be full nodes around when they need them.
And then they complain that sync is slow... 

Getting payed to run a full node is a good way to earn ZTTL for those that don't want to mine (or find it too hard)

More nodes will make the network more secure and improve connectivity for all wallets. Everything will sync faster.