Springboot defaults to Jetty startup without configuration. Why?

previously used and online materials are enabled by default to use tomcat;
recently, when building Springboot, tomcat, was not excluded and jetty dependency was not introduced, but Jetty was used to start by default at startup.

the following are the dependencies introduced by pom:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
    <scope>test</scope>
</dependency>
<!--spring-->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
<!--<dependency>-->
    <!--<groupId>org.springframework.boot</groupId>-->
    <!--<artifactId>spring-boot-starter-redis</artifactId>-->
    <!--<version>1.3.0.RELEASE</version>-->
<!--</dependency>-->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-security</artifactId>
</dependency>
<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.4</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.apache.commons/commons-lang3 -->
<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.7</version>
</dependency>
<!-- https://mvnrepository.com/artifact/io.springfox/springfox-swagger2 -->
<!--API-->
<dependency>
    <groupId>io.springfox</groupId>
    <artifactId>springfox-swagger2</artifactId>
    <version>2.7.0</version>
</dependency>
<!-- https://mvnrepository.com/artifact/io.springfox/springfox-swagger-ui -->
<dependency>
    <groupId>io.springfox</groupId>
    <artifactId>springfox-swagger-ui</artifactId>
    <version>2.7.0</version>
</dependency>
<!-- https://mvnrepository.com/artifact/com.github.tomakehurst/wiremock -->
<!--Rest-->
<dependency>
    <groupId>com.github.tomakehurst</groupId>
    <artifactId>wiremock</artifactId>
    <version>2.12.0</version>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>

<!---->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-configuration-processor</artifactId>
    <optional>true</optional>
</dependency>
<!--query dsl end-->
<dependency>
    <groupId>javax.mail</groupId>
    <artifactId>mail</artifactId>
    <version>1.5.0-b01</version>
</dependency>
<!--oauth2.0-->
<dependency>
    <groupId>org.springframework.security.oauth</groupId>
    <artifactId>spring-security-oauth2</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.security</groupId>
    <artifactId>spring-security-jwt</artifactId>
</dependency>