Actors from outside the system that want bitcoin to die, can spam it to death - AND include the blocks on their own / at their own expense, because the cost of bitcoin back in 2010 was peanuts.
The point is that by PoW consensus, every previous block is voted over by PoW by the peer miners. So if the PoW consensus is working, you might think that even if a crazy attacker makes a 10 GB block that is correct according to the bitcoin protocol, the next miner should most probably decide NOT to build upon it because he estimates this not to be the good consensus of the bitcoin state.
But another miner might see that another block was issued as #xxxxx instead of the 10gb block and then reject that one for not building upon the 10gb one. So it's a gamble that others will do the same...