This is as @suren says due to the fact that you do not provision a default page with your onet.xml
If you do not want to customize the default page you can activate the WikiPage HomePage Feature, it is a web scoped feature, so add it under <WebFeatures>
in your onet.xml
<!-- WikiPageHomePage Feature -->
<Feature ID="00BFEA71-D8FE-4FEC-8DAD-01C19A6E4053" />
To make your new site have all the abilities of a standard teamsite you would need to activate the following features:
<SiteFeatures>
<!-- BasicWebParts Feature -->
<Feature ID="00BFEA71-1C5E-4A24-B310-BA51C3EB7A57" />
<!-- Three-state Workflow Feature -->
<Feature ID="FDE5D850-671E-4143-950A-87B473922DC7" />
</SiteFeatures>
<WebFeatures>
<!-- TeamCollab Feature -->
<Feature ID="00BFEA71-4EA5-48D4-A4AD-7EA5C011ABE5" />
<!-- MobilityRedirect -->
<Feature ID="F41CC668-37E5-4743-B4A8-74D1DB3FD8A4" />
<!-- WikiPageHomePage Feature -->
<Feature ID="00BFEA71-D8FE-4FEC-8DAD-01C19A6E4053" />
<!-- SiteNotebook Feature -->
<Feature ID="F151BB39-7C3B-414F-BB36-6BF18872052F" />
<!-- Getting Started List instance -->
<Feature ID="4AEC7207-0D02-4f4f-AA07-B370199CD0C7" />
<!-- MDS -->
<Feature ID="87294C72-F260-42f3-A41B-981A2FFCE37A" />
</WebFeatures>
You find this in the ONET.XML found in 15/TEMPLATE/SiteTemplates/sts/xml
Edit:
If you want a default page just like the one for a Team Site, with webparts and all:
- Add a module to your project
- Add that one to a feature that is web
scoped and activate it in the ONET.XML webscoped features.
- In the module, add the default.aspx from
15/TEMPLATE/SiteTemplates/sts/
In the Elements.xml of the module add the following (substituting the module name and file path to match your module):
<?xml version="1.0" encoding="utf-8"?>
<Elements xmlns="http://schemas.microsoft.com/sharepoint/">
<Module Name="ProjectDefault" Url="" Path="">
<File Path="ProjectDefault\default.aspx" Url="default.aspx" NavBarHome="True">
<AllUsersWebPart WebPartZoneID="Top" WebPartOrder="1">
<![CDATA[
<webParts>
<webPart xmlns="http://schemas.microsoft.com/WebPart/v3">
<metaData>
<type name="Microsoft.SharePoint.Portal.WebControls.ProjectSummaryWebPart, Microsoft.SharePoint.Portal, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" />
<importErrorMessage>$Resources:spscore,WPImportErrorMessage;</importErrorMessage>
</metaData>
<data>
<properties>
<property name="Title" type="string">$Resources:spscore,ProjectSummaryWebPartTitle;</property>
<property name="Description" type="string">$Resources:spscore,ProjectSummaryWebPartDescription;</property>
<property name="ChromeType" type="chrometype">None</property>
</properties>
</data>
</webPart>
</webParts>
]]>
</AllUsersWebPart>
<AllUsersWebPart WebPartZoneID="Left" WebPartOrder="1">
<![CDATA[
<WebPart xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.microsoft.com/WebPart/v2">
<Title>Site Feed</Title>
<FrameType>None</FrameType>
<Description>Site Feed contains microblogging conversations on a group site. </Description>
<IsIncluded>true</IsIncluded>
<ZoneID>Left</ZoneID>
<PartOrder>0</PartOrder>
<FrameState>Normal</FrameState>
<Height />
<Width />
<AllowRemove>true</AllowRemove>
<AllowZoneChange>true</AllowZoneChange>
<AllowMinimize>true</AllowMinimize>
<AllowConnect>true</AllowConnect>
<AllowEdit>true</AllowEdit>
<AllowHide>true</AllowHide>
<IsVisible>true</IsVisible>
<DetailLink />
<HelpLink />
<HelpMode>Modeless</HelpMode>
<Dir>Default</Dir>
<PartImageSmall />
<MissingAssembly>Cannot import this Web Part.</MissingAssembly>
<PartImageLarge />
<IsIncludedFilter />
<Assembly>Microsoft.SharePoint.Portal, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c</Assembly>
<TypeName>Microsoft.SharePoint.Portal.WebControls.SiteFeedWebPart</TypeName>
</WebPart>]]>
</AllUsersWebPart>
<View List="$Resources:core,shareddocuments_Folder;" BaseViewID="1" WebPartZoneID="Right" />
</File>