Catholics are supposed to believe that they receive the actual body and blood of Jesus at Holy Communion, and this is where the Catholic Mass differs from a CoE service. This 'food for the soul' is very important to Catholics, and Christ's sacrifice is central to every Mass. Many people don't know this or don't believe it. Of course, faith without good works is nothing, so the Bible says, and vice versa. Also, it is true that many Catholics attend out of duty without getting involved in parish activities, while parish priests do not always reach out to the people these days. It is little wonder therefore, that they feel the church does nothing for them.
It is not for anyone to judge, and I do know people who have changed churches for a whole variety of reasons, often for the 'welcome' aspect or because they don't like the priest. I'd say, at least they are continuing with their faith and have thought deeply about their decision. I can't see myself ever switching churches, despite disagreeing with the Catholic church's exclusion of women from the diaconate and priesthood, but I have seen a distinct change in attitude over the years. I think any institution will have its problems because it is made up of people with all their faults. I happily attend services of other denominations on occasion, and in our town there is a strong ecumenism amongst the many denominations, which I think is very healthy.