One can add to ALB multiple listeners and rules that can check for hostname and forward requests to appropriate target groups. So, I'm not sure what could be the point in using more than 1 Application Load Balancer, if I can just add a new rule?
The ALB has a limit on how many hosts it can support. If your services does not fit within these limits, you'll need to use more than 1 ALB. https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-limits.html
The most prohibitive one is probably the certificate limit, which will restrict the maximum number of HTTPS hosts to 25.
You also the security group limit, which is 5 per ALB. If you were to set up your hosts serving your domains within 5 SG, it would work, but not best practices.
If you only need HTTP, you can get away with 100 domains, per
Rules per load balancer (not counting default rules): 100
And even if your service falls within all these, you have a limit of 1000 targets per ALB, which would be a pain to manage during a spike.