Not many people were mining with high-tech mining machines when Bitcoin was released (2009, if I'm not mistaken).
Thus, bitcoin was vulnerable to a 51% attack by a big company or an individual with huge resources.
But was there any such attack on Bitcoin around that time?
But back then the value of bitcoin is close to few dollars so why would even try such things especially it will not have any benefit for them once they lose 51% hash rate power the blocks will be back and all the malicious blocks will be replaced by actual one.
They care only if the price is higher ironically the expense of 51% attacks also higher enough for not to attempt such attacks on the bitcoin network which is what keeping the bitcoin standout from other shitcoins.