Unable to retrieve all EC2 instances

I'm writing a code to get EC2 On-Demand prices for a particular OS in a determined region (eg. 'Ubuntu Pro' and 'us-east-1') but I only get 661 instances out of the 705 available on the pricing list. Is there a way that I can retrieve all the instances available for said region and OS - with the correct price?

Pricing list:

Database:

Python Code:

import boto3
import json
import os
from database import insert_into_table

def ec2_prices(region, op_system, database_name, table_name):
    desired_region = region
    pricing_region = 'us-east-1'

    ec2            = boto3.client('ec2', region_name=desired_region)
    pricing_client = boto3.client('pricing', region_name=pricing_region)

    response       = ec2.describe_instance_type_offerings(LocationType='region')
    instance_types = [instance_type['InstanceType'] for instance_type in response['InstanceTypeOfferings']]
      
    for instance_type in instance_types:
        response = pricing_client.get_products(
            ServiceCode='AmazonEC2',
            Filters=[
                {'Type': 'TERM_MATCH', 'Field': 'instanceType', 'Value': instance_type},
                {'Type': 'TERM_MATCH', 'Field': 'operatingSystem', 'Value': op_system},
            ],
        )
        for product in response['PriceList']:
            product_dict         = json.loads(product)
            attributes           = product_dict.get('product').get('attributes')
            
            instance_region      = attributes.get('regionCode')
            instance_region_name = attributes.get('location')
            instance_memory      = attributes.get('memory')[:-3]
            instance_vcpu        = attributes.get('vcpu')
            instance_os          = attributes.get('operatingSystem')
            tenancy              = attributes.get('tenancy')
            
            if instance_region == desired_region and tenancy == 'Shared':
                terms = product_dict.get('terms', {}).get('OnDemand', {})
  
                for term_key, term_value in terms.items():
                    price_dimensions = term_value['priceDimensions']

                    for _, price_dimension_value in price_dimensions.items():
                        price       = price_dimension_value['pricePerUnit']  
                        description = price_dimension_value['description']                      
                        value       = float(price.get('USD', 0))
                        
                        if value > 0 and f'{op_system} {instance_type}' in description:                            
                            insert_into_table(
                                database_name, 
                                table_name, 
                                instance_type, 
                                value, 
                                instance_region, 
                                instance_vcpu, 
                                instance_memory, 
                                instance_os
                            )

There are some tags (tenancy and description) that are used for retrieving the right price for the instance.