Why is blockchain necessary? I'm trying really hard to understand how bitcoin works.

I understand that bitcoin miners does proof of work, and creates blocks, and then transactions are sealed inside this block to become "confirmed". And this has something to do with double spending.. somehow..

So, my questions is, why cant we do a similar decentralized network, without proof of work/blockchain? In this network, we just keep a list of all transactions (akin to blockchain) (a copy for each node), and then use majority rule. Ie, if there is a dispute in the new transaction, we just go to every node, check their list of all transactions, and if the new transaction contradicts majority of list of all transactions, then the new transaction will be rejected etc. And nobody need to solve any hard math problems (ie proof of work)

And for new transactions, our protocol can be following: If nobody disputes the transaction over the next 60minutes, then we set confirmed flag of this transaction to be 1, and thus this transaction is now confirmed etc.

In other words, im struggling to understand the value of proof-of-work process in bitcoin.
I think the introduction of block has much more a security-related origin:

Currently, getting transactions confirmed costs a certain amount of work for which computer have to run a long time and cost some time, effort and money. Because of this, it is hard to manipulate the chain of transactions. It is hard to find a correct block with a certain set of transactions and cheating will result in your block being refused by the network.

However, when clients just keep lots of transactions, it would be much easier to f.e. set up thousands of false nodes that manipulate the network. A node that only requires memory is much cheaper than one that requires hashpower. With some resources it's easy to add thousands to hundreds of thousands of clients (these don't have to be separate machines but can be virtual ones) participating and entering bogus transactions or leaving some out.

The fact that creating the blocks is "difficult" add a lot of security to the network, making it extremely hard to falsely manipulate the transaction history.