As we can see this would result in a geminate /dd/ in the first example and a geminate /tt/ in the second. When I'm teaching English to language students, I like to point out that this would make the final /d/ or /t/ ending difficult to distinguish (and if we wanted to release the first /t/ or /d/ before the second, difficult to pronounce). However, this is not a good argument for why this doesn't happen in English. Firstly, it does not seem to be very important to hear or pronounce past tense endings in English. If the base form of a verb ends in a consonant, then we are always allowed to omit regular /t/ or /d/ endings in spoken English so long as the following word begins with a consonant. Additionally, many irregular verbs in English have a past tense which is identical to the base form or present tense, for example, the verbs cut or put—we just tell which is which from the context. The real reason might seem to be just that English never allows geminate consonants in the first place.