They failed. Repeatedly. For decades. They spent billions trying. The failed so much that the standard writers determined the only logical conclusion is that it must be practically impossible to retrofit a system that failed EAL5 certification to achieve EAL5 or higher certification without a complete rewrite and redesign. It says so right there in the standard [1]: "EAL4 is the highest level at which it is likely to be economically feasible to retrofit to an existing product line". That was added due to the decades of experience where everybody who ever tried to do that failed no matter how much time or money they spent.
We also have plenty of evidence that it does matter, they just can not do it. Here is Google touting their Common Criteria certification for the Titan M2 security chip hardware which is EAL4 + AVA_VAN.5 (resistance against penetration attackers with a high attack potential) [2]. Note that this is only the hardware (software was not certified; a critical severity vulnerability was actually disclosed in the software allowing complete takeover if I remember correctly) and only cherry picks AVA_VAN.5 so is still only EAL4, not a holistic EAL6 certification. Getting that certification was a deliberate effort and cost. If they literally did not care about the Common Criteria then they would just certify to the checkbox level like everybody else. It is because they could certify it to a higher level than most other can achieve that they chose to do it because then they could tout their unique advantage.
Basically everybody gets a certification and basically everybody displays their certification on their page. There is something to be said about them opting for a EAL1 over a EAL4. It is basically assumed that any serious vendor could probably get a EAL4 with some effort. So, there is no differential advantage to displaying a EAL4 since everybody could get it. It is just a zero-sum game to pay for certification if everybody knows nobody has a true advantage. However, if you can achieve EAL5 or higher, then you do have a unique advantage because basically nobody else can do it. The fact that none of the major vendors attempts EAL5, shows that they can not do it.
[1] https://www.commoncriteriaportal.org/files/ccfiles/CC2022PAR... Page 18
[2] https://security.googleblog.com/2022/10/google-pixel-7-and-p...