You certainly can if you fulfill the criterias which involves technical knowledge and financial commitment - two of the aspect that only few people are able or want to meet. An important aspect of a masternode is the minimum amount a node must meet. For a Dash Masternode, for example, 1000 coins are necessary.
If a masternode does not meet the minimum requirement, it no longer qualifies as a master node and loses its privileges. This minimum amount always involves a certain amount of coins in the network. Depending on the price of the coin, this amount can be very high to cover as individual. In addition to that, you have to have the needed technical equipment and knowledge.
The more diversified you want to set up your Masternode portfolio, the higher the capital requirements of the individual. The higher the own capital requirement, the higher the risk share in the crypto market. A masternode pool thus offers maximum diversification (distribution) of the risk.