The horse manure and dead horses alone made them disgusting disease ridden nightmares.
https://www.newyorkalmanack.com/2021/02/the-unpleasant-side-of-life-with-horses-in-cities/
https://99percentinvisible.org/article/cities-paved-dung-urban-design-great-horse-manure-crisis-1894/
America didn't destroy its own cities - those cities were surpassed when they no longer supported the few industries they once did. There are few if any industries that are better served currently within a city.
Accommodation and Food Services Administrative and Support and Waste Management and Remediation ServicesAdministrative and Support ServicesAgriculture, Forestry, Fishing and HuntingAir TransportationAmbulatory Health Care ServicesAmusement, Gambling, and Recreation IndustriesAnimal ProductionApparel Manufacturing
Arts, Entertainment, and Recreation - Some Arts but Entertainment and Recreation are outside cities. Beverage and Tobacco Product Manufacturing
Broadcasting - Was for decades but podcasters can and do broadcast from anywhere Building Material and Garden Equipment and Supplies DealersChemical ManufacturingClothing and Clothing Accessories StoresComputer and Electronic Product ManufacturingConstruction
Construction of Buildings
Couriers and Messengers Credit Intermediation and Related ActivitiesCrop ProductionData Processing, Hosting, and Related ServicesEducation and Health Services
Educational Services - mixed. Larger campuses are outside cities Electrical Equipment, Appliance, and Component ManufacturingElectronics and Appliance StoresFabricated Metal Product Manufacturing
Finance and Insurance - this has been shifting more and more to outside cities Financial ActivitiesFishing, Hunting and TrappingFood and Beverage StoresFood Manufacturing
Food Services and Drinking Places Forestry and LoggingFunds, Trusts, and Other Financial VehiclesFurniture and Home Furnishings StoresFurniture and Related Product ManufacturingGasoline StationsGeneral Merchandise StoresGoods-Producing IndustriesHealth and Personal Care StoresHealth Care and Social AssistanceHeavy and Civil Engineering Construction
Hospitals - some due to population density although more and more are large campuses outside cities InformationInsurance Carriers and Related ActivitiesInternet Publishing and BroadcastingLeather and Allied Product ManufacturingLeisure and HospitalityLessors of Nonfinancial Intangible AssetsMachinery Manufacturing
Management of Companies and Enterprises ManufacturingMerchant Wholesalers, Durable GoodsMerchant Wholesalers, Nondurable GoodsMining (except Oil and Gas) (NAICS 212)Mining, Quarrying, and Oil and Gas ExtractionMiscellaneous ManufacturingMiscellaneous Store RetailersMonetary Authorities - Central BankMotion Picture and Sound Recording IndustriesMotor Vehicle and Parts DealersMuseums, Historical Sites, and Similar InstitutionsNatural Resources and MiningNonmetallic Mineral Product ManufacturingNonstore RetailersNursing and Residential Care FacilitiesOil and Gas ExtractionOther Information ServicesOther ServicesPaper Manufacturing
Performing Arts, Spectator Sports, and Related Industries - Performing Arts; yes. Sports and others definitely outside cities. Personal and Laundry ServicesPetroleum and Coal Products ManufacturingPipeline TransportationPlastics and Rubber Products ManufacturingPostal ServicePrimary Metal ManufacturingPrinting and Related Support ActivitiesPrivate HouseholdsProfessional and Business ServicesProfessional, Scientific, and Technical ServicesPublishing Industries
Rail Transportation - passenger rail in cities runs at a loss and is subsidized by vehicles Real EstateReal Estate and Rental and LeasingReligious, Grantmaking, Civic, Professional, and Similar OrganizationsRental and Leasing ServicesRepair and MaintenanceRetail TradeScenic and Sightseeing Transportation
Securities, Commodity Contracts, and Other Financial Investments and Related Activities - more of this is relocating outside cities Service-Providing IndustriesSocial AssistanceSpecialty Trade ContractorsSporting Goods, Hobby, Book, and Music StoresSupport Activities for Agriculture and ForestrySupport Activities for MiningSupport Activities for TransportationTelecommunicationsTextile MillsTextile Product MillsTrade, Transportation, and Utilities
Transit and Ground Passenger Transportation - This runs at a loss in cities and has to subsidized by others. Transportation and WarehousingTransportation Equipment ManufacturingTruck TransportationUtilitiesWarehousing and StorageWaste Management and Remediation ServicesWater TransportationWholesale Electronic Markets and Agents and BrokersWholesale TradeWood Product Manufacturing